================
Deployment Guide
================

-----------------------
Hardware Considerations
-----------------------

Swift is designed to run on commodity hardware. At Rackspace, our storage
servers are currently running fairly generic 4U servers with 24 2T SATA
drives and 8 cores of processing power. RAID on the storage drives is not
required and not recommended. Swift's disk usage pattern is the worst
case possible for RAID, and performance degrades very quickly using RAID 5
or 6.

------------------
Deployment Options
------------------

The swift services run completely autonomously, which provides for a lot of
flexibility when architecting the hardware deployment for swift. The 4 main
services are:

#. Proxy Services
#. Object Services
#. Container Services
#. Account Services

The Proxy Services are more CPU and network I/O intensive. If you are using
10g networking to the proxy, or are terminating SSL traffic at the proxy,
greater CPU power will be required.

The Object, Container, and Account Services (Storage Services) are more disk
and network I/O intensive.

The easiest deployment is to install all services on each server. There is
nothing wrong with doing this, as it scales each service out horizontally.

At Rackspace, we put the Proxy Services on their own servers and all of the
Storage Services on the same server. This allows us to send 10g networking to
the proxy and 1g to the storage servers, and keep load balancing to the
proxies more manageable.  Storage Services scale out horizontally as storage
servers are added, and we can scale overall API throughput by adding more
Proxies.

If you need more throughput to either Account or Container Services, they may
each be deployed to their own servers. For example you might use faster (but
more expensive) SAS or even SSD drives to get faster disk I/O to the databases.

Load balancing and network design is left as an exercise to the reader,
but this is a very important part of the cluster, so time should be spent
designing the network for a Swift cluster.

.. _ring-preparing:

------------------
Preparing the Ring
------------------

The first step is to determine the number of partitions that will be in the
ring. We recommend that there be a minimum of 100 partitions per drive to
insure even distribution across the drives. A good starting point might be
to figure out the maximum number of drives the cluster will contain, and then
multiply by 100, and then round up to the nearest power of two.

For example, imagine we are building a cluster that will have no more than
5,000 drives. That would mean that we would have a total number of 500,000
partitions, which is pretty close to 2^19, rounded up.

It is also a good idea to keep the number of partitions small (relatively).
The more partitions there are, the more work that has to be done by the
replicators and other backend jobs and the more memory the rings consume in
process. The goal is to find a good balance between small rings and maximum
cluster size.

The next step is to determine the number of replicas to store of the data.
Currently it is recommended to use 3 (as this is the only value that has
been tested). The higher the number, the more storage that is used but the
less likely you are to lose data.

It is also important to determine how many zones the cluster should have. It is
recommended to start with a minimum of 5 zones. You can start with fewer, but
our testing has shown that having at least five zones is optimal when failures
occur. We also recommend trying to configure the zones at as high a level as
possible to create as much isolation as possible. Some example things to take
into consideration can include physical location, power availability, and
network connectivity. For example, in a small cluster you might decide to
split the zones up by cabinet, with each cabinet having its own power and
network connectivity. The zone concept is very abstract, so feel free to use
it in whatever way best isolates your data from failure. Zones are referenced
by number, beginning with 1.

You can now start building the ring with::

    swift-ring-builder <builder_file> create <part_power> <replicas> <min_part_hours>

This will start the ring build process creating the <builder_file> with
2^<part_power> partitions. <min_part_hours> is the time in hours before a
specific partition can be moved in succession (24 is a good value for this).

Devices can be added to the ring with::

    swift-ring-builder <builder_file> add z<zone>-<ip>:<port>/<device_name>_<meta> <weight>

This will add a device to the ring where <builder_file> is the name of the
builder file that was created previously, <zone> is the number of the zone
this device is in, <ip> is the ip address of the server the device is in,
<port> is the port number that the server is running on, <device_name> is
the name of the device on the server (for example: sdb1), <meta> is a string
of metadata for the device (optional), and <weight> is a float weight that
determines how many partitions are put on the device relative to the rest of
the devices in the cluster (a good starting point is 100.0 x TB on the drive).
Add each device that will be initially in the cluster.

Once all of the devices are added to the ring, run::

    swift-ring-builder <builder_file> rebalance

This will distribute the partitions across the drives in the ring. It is
important whenever making changes to the ring to make all the changes
required before running rebalance. This will ensure that the ring stays as
balanced as possible, and as few partitions are moved as possible.

The above process should be done to make a ring for each storage service
(Account, Container and Object). The builder files will be needed in future
changes to the ring, so it is very important that these be kept and backed up.
The resulting .tar.gz ring file should be pushed to all of the servers in the
cluster. For more information about building rings, running
swift-ring-builder with no options will display help text with available
commands and options. More information on how the ring works internally
can be found in the :doc:`Ring Overview <overview_ring>`.

----------------------------
General Server Configuration
----------------------------

Swift uses paste.deploy (http://pythonpaste.org/deploy/) to manage server
configurations. Default configuration options are set in the `[DEFAULT]`
section, and any options specified there can be overridden in any of the other
sections BUT ONLY BY USING THE SYNTAX ``set option_name = value``. This is the
unfortunate way paste.deploy works and I'll try to explain it in full.

First, here's an example paste.deploy configuration file::

    [DEFAULT]
    name1 = globalvalue
    name2 = globalvalue
    name3 = globalvalue
    set name4 = globalvalue

    [pipeline:main]
    pipeline = myapp

    [app:myapp]
    use = egg:mypkg#myapp
    name2 = localvalue
    set name3 = localvalue
    set name5 = localvalue
    name6 = localvalue

The resulting configuration that myapp receives is::

    global {'__file__': '/etc/mypkg/wsgi.conf', 'here': '/etc/mypkg',
            'name1': 'globalvalue',
            'name2': 'globalvalue',
            'name3': 'localvalue',
            'name4': 'globalvalue',
            'name5': 'localvalue',
            'set name4': 'globalvalue'}
    local {'name6': 'localvalue'}

So, `name1` got the global value which is fine since it's only in the `DEFAULT`
section anyway.

`name2` got the global value from `DEFAULT` even though it appears to be
overridden in the `app:myapp` subsection. This is just the unfortunate way
paste.deploy works (at least at the time of this writing.)

`name3` got the local value from the `app:myapp` subsection because it is using
the special paste.deploy syntax of ``set option_name = value``. So, if you want
a default value for most app/filters but want to overridde it in one
subsection, this is how you do it.

`name4` got the global value from `DEFAULT` since it's only in that section
anyway. But, since we used the ``set`` syntax in the `DEFAULT` section even
though we shouldn't, notice we also got a ``set name4`` variable. Weird, but
probably not harmful.

`name5` got the local value from the `app:myapp` subsection since it's only
there anyway, but notice that it is in the global configuration and not the
local configuration. This is because we used the ``set`` syntax to set the
value. Again, weird, but not harmful since Swift just treats the two sets of
configuration values as one set anyway.

`name6` got the local value from `app:myapp` subsection since it's only there,
and since we didn't use the ``set`` syntax, it's only in the local
configuration and not the global one. Though, as indicated above, there is no
special distinction with Swift.

That's quite an explanation for something that should be so much simpler, but
it might be important to know how paste.deploy interprets configuration files.
The main rule to remember when working with Swift configuration files is:

.. note::

    Use the ``set option_name = value`` syntax in subsections if the option is
    also set in the ``[DEFAULT]`` section. Don't get in the habit of always
    using the ``set`` syntax or you'll probably mess up your non-paste.deploy
    configuration files.


---------------------------
Object Server Configuration
---------------------------

An Example Object Server configuration can be found at
etc/object-server.conf-sample in the source code repository.

The following configuration options are available:

[DEFAULT]

===================  ==========  =============================================
Option               Default     Description
-------------------  ----------  ---------------------------------------------
swift_dir            /etc/swift  Swift configuration directory
devices              /srv/node   Parent directory of where devices are mounted
mount_check          true        Whether or not check if the devices are
                                 mounted to prevent accidentally writing
                                 to the root device
bind_ip              0.0.0.0     IP Address for server to bind to
bind_port            6000        Port for server to bind to
workers              1           Number of workers to fork
disable_fallocate    false       Disable "fast fail" fallocate checks if the
                                 underlying filesystem does not support it.
log_custom_handlers  None        Comma-separated list of functions to call
                                 to setup custom log handlers.
===================  ==========  =============================================

[object-server]

==================  =============  ===========================================
Option              Default        Description
------------------  -------------  -------------------------------------------
use                                paste.deploy entry point for the object
                                   server.  For most cases, this should be
                                   `egg:swift#object`.
set log_name        object-server  Label used when logging
set log_facility    LOG_LOCAL0     Syslog log facility
set log_level       INFO           Logging level
set log_requests    True           Whether or not to log each request
user                swift          User to run as
node_timeout        3              Request timeout to external services
conn_timeout        0.5            Connection timeout to external services
network_chunk_size  65536          Size of chunks to read/write over the
                                   network
disk_chunk_size     65536          Size of chunks to read/write to disk
max_upload_time     86400          Maximum time allowed to upload an object
slow                0              If > 0, Minimum time in seconds for a PUT
                                   or DELETE request to complete
mb_per_sync         512            On PUT requests, sync file every n MB
keep_cache_size     5242880        Largest object size to keep in buffer cache
keep_cache_private  false          Allow non-public objects to stay in
                                   kernel's buffer cache
==================  =============  ===========================================

[object-replicator]

==================  =================  =======================================
Option              Default            Description
------------------  -----------------  ---------------------------------------
log_name            object-replicator  Label used when logging
log_facility        LOG_LOCAL0         Syslog log facility
log_level           INFO               Logging level
daemonize           yes                Whether or not to run replication as a
                                       daemon
run_pause           30                 Time in seconds to wait between
                                       replication passes
concurrency         1                  Number of replication workers to spawn
timeout             5                  Timeout value sent to rsync --timeout
                                       and --contimeout options
stats_interval      3600               Interval in seconds between logging
                                       replication statistics
reclaim_age         604800             Time elapsed in seconds before an
                                       object can be reclaimed
==================  =================  =======================================

[object-updater]

==================  ==============  ==========================================
Option              Default         Description
------------------  --------------  ------------------------------------------
log_name            object-updater  Label used when logging
log_facility        LOG_LOCAL0      Syslog log facility
log_level           INFO            Logging level
interval            300             Minimum time for a pass to take
concurrency         1               Number of updater workers to spawn
node_timeout        10              Request timeout to external services
conn_timeout        0.5             Connection timeout to external services
slowdown            0.01            Time in seconds to wait between objects
==================  ==============  ==========================================

[object-auditor]

==================  ==============  ==========================================
Option              Default         Description
------------------  --------------  ------------------------------------------
log_name            object-auditor  Label used when logging
log_facility        LOG_LOCAL0      Syslog log facility
log_level           INFO            Logging level
log_time            3600            Frequency of status logs in seconds.
files_per_second    20              Maximum files audited per second. Should
                                    be tuned according to individual system
                                    specs. 0 is unlimited.
bytes_per_second    10000000        Maximum bytes audited per second. Should
                                    be tuned according to individual system
                                    specs. 0 is unlimited.
==================  ==============  ==========================================

------------------------------
Container Server Configuration
------------------------------

An example Container Server configuration can be found at
etc/container-server.conf-sample in the source code repository.

The following configuration options are available:

[DEFAULT]

===================  ==========  ============================================
Option               Default     Description
-------------------  ----------  --------------------------------------------
swift_dir            /etc/swift  Swift configuration directory
devices              /srv/node   Parent directory of where devices are mounted
mount_check          true        Whether or not check if the devices are
                                 mounted to prevent accidentally writing
                                 to the root device
bind_ip              0.0.0.0     IP Address for server to bind to
bind_port            6001        Port for server to bind to
workers              1           Number of workers to fork
user                 swift       User to run as
disable_fallocate    false       Disable "fast fail" fallocate checks if the
                                 underlying filesystem does not support it.
log_custom_handlers  None        Comma-separated list of functions to call
                                 to setup custom log handlers.
===================  ==========  ============================================

[container-server]

==================  ================  ========================================
Option              Default           Description
------------------  ----------------  ----------------------------------------
use                                   paste.deploy entry point for the
                                      container server.  For most cases, this
                                      should be `egg:swift#container`.
set log_name        container-server  Label used when logging
set log_facility    LOG_LOCAL0        Syslog log facility
set log_level       INFO              Logging level
node_timeout        3                 Request timeout to external services
conn_timeout        0.5               Connection timeout to external services
allow_versions      false             Enable/Disable object versioning feature
==================  ================  ========================================

[container-replicator]

==================  ====================  ====================================
Option              Default               Description
------------------  --------------------  ------------------------------------
log_name            container-replicator  Label used when logging
log_facility        LOG_LOCAL0            Syslog log facility
log_level           INFO                  Logging level
per_diff            1000
concurrency         8                     Number of replication workers to
                                          spawn
run_pause           30                    Time in seconds to wait between
                                          replication passes
node_timeout        10                    Request timeout to external services
conn_timeout        0.5                   Connection timeout to external
                                          services
reclaim_age         604800                Time elapsed in seconds before a
                                          container can be reclaimed
==================  ====================  ====================================

[container-updater]

========================  =================  ==================================
Option                    Default            Description
------------------------  -----------------  ----------------------------------
log_name                  container-updater  Label used when logging
log_facility              LOG_LOCAL0         Syslog log facility
log_level                 INFO               Logging level
interval                  300                Minimum time for a pass to take
concurrency               4                  Number of updater workers to spawn
node_timeout              3                  Request timeout to external
                                             services
conn_timeout              0.5                Connection timeout to external
                                             services
slowdown                  0.01               Time in seconds to wait between
                                             containers
account_suppression_time  60                 Seconds to suppress updating an
                                             account that has generated an
                                             error (timeout, not yet found,
                                             etc.)
========================  =================  ==================================

[container-auditor]

==================  =================  =======================================
Option              Default            Description
------------------  -----------------  ---------------------------------------
log_name            container-auditor  Label used when logging
log_facility        LOG_LOCAL0         Syslog log facility
log_level           INFO               Logging level
interval            1800               Minimum time for a pass to take
==================  =================  =======================================

----------------------------
Account Server Configuration
----------------------------

An example Account Server configuration can be found at
etc/account-server.conf-sample in the source code repository.

The following configuration options are available:

[DEFAULT]

===================  ==========  =============================================
Option               Default     Description
-------------------  ----------  ---------------------------------------------
swift_dir            /etc/swift  Swift configuration directory
devices              /srv/node   Parent directory or where devices are mounted
mount_check          true        Whether or not check if the devices are
                                 mounted to prevent accidentally writing
                                 to the root device
bind_ip              0.0.0.0     IP Address for server to bind to
bind_port            6002        Port for server to bind to
workers              1           Number of workers to fork
user                 swift       User to run as
db_preallocation     off         If you don't mind the extra disk space usage in
                                 overhead, you can turn this on to preallocate
                                 disk space with SQLite databases to decrease
                                 fragmentation.
disable_fallocate    false       Disable "fast fail" fallocate checks if the
                                 underlying filesystem does not support it.
log_custom_handlers  None        Comma-separated list of functions to call
                                 to setup custom log handlers.
===================  ==========  =============================================

[account-server]

==================  ==============  ==========================================
Option              Default         Description
------------------  --------------  ------------------------------------------
use                                 Entry point for paste.deploy for the account
                                    server.  For most cases, this should be
                                    `egg:swift#account`.
set log_name        account-server  Label used when logging
set log_facility    LOG_LOCAL0      Syslog log facility
set log_level       INFO            Logging level
==================  ==============  ==========================================

[account-replicator]

==================  ==================  ======================================
Option              Default             Description
------------------  ------------------  --------------------------------------
log_name            account-replicator  Label used when logging
log_facility        LOG_LOCAL0          Syslog log facility
log_level           INFO                Logging level
per_diff            1000
concurrency         8                   Number of replication workers to spawn
run_pause           30                  Time in seconds to wait between
                                        replication passes
node_timeout        10                  Request timeout to external services
conn_timeout        0.5                 Connection timeout to external services
reclaim_age         604800              Time elapsed in seconds before an
                                        account can be reclaimed
==================  ==================  ======================================

[account-auditor]

====================  ===============  =======================================
Option                Default          Description
--------------------  ---------------  ---------------------------------------
log_name              account-auditor  Label used when logging
log_facility          LOG_LOCAL0       Syslog log facility
log_level             INFO             Logging level
interval              1800             Minimum time for a pass to take
====================  ===============  =======================================

[account-reaper]

==================  ===============  =========================================
Option              Default          Description
------------------  ---------------  -----------------------------------------
log_name            account-auditor  Label used when logging
log_facility        LOG_LOCAL0       Syslog log facility
log_level           INFO             Logging level
concurrency         25               Number of replication workers to spawn
interval            3600             Minimum time for a pass to take
node_timeout        10               Request timeout to external services
conn_timeout        0.5              Connection timeout to external services
delay_reaping       0                Normally, the reaper begins deleting
                                     account information for deleted accounts
                                     immediately; you can set this to delay
                                     its work however. The value is in seconds,
                                     2592000 = 30 days, for example.
==================  ===============  =========================================

--------------------------
Proxy Server Configuration
--------------------------

An example Proxy Server configuration can be found at
etc/proxy-server.conf-sample in the source code repository.

The following configuration options are available:

[DEFAULT]

============================  ===============  =============================
Option                        Default          Description
----------------------------  ---------------  -----------------------------
bind_ip                       0.0.0.0          IP Address for server to
                                               bind to
bind_port                     80               Port for server to bind to
swift_dir                     /etc/swift       Swift configuration directory
workers                       1                Number of workers to fork
user                          swift            User to run as
cert_file                                      Path to the ssl .crt. This
                                               should be enabled for testing
                                               purposes only.
key_file                                       Path to the ssl .key. This
                                               should be enabled for testing
                                               purposes only.
cors_allow_origin                              This is a list of hosts that
                                               are included with any CORS 
                                               request by default and 
                                               returned with the 
                                               Access-Control-Allow-Origin
                                               header in addition to what
                                               the container has set.
log_custom_handlers           None             Comma separated list of functions
                                               to call to setup custom log
                                               handlers.
============================  ===============  =============================

[proxy-server]

============================  ===============  =============================
Option                        Default          Description
----------------------------  ---------------  -----------------------------
use                                            Entry point for paste.deploy for
                                               the proxy server.  For most
                                               cases, this should be
                                               `egg:swift#proxy`.
set log_name                  proxy-server     Label used when logging
set log_facility              LOG_LOCAL0       Syslog log facility
set log_level                 INFO             Log level
set log_headers               True             If True, log headers in each
                                               request
set log_handoffs              True             If True, the proxy will log
                                               whenever it has to failover to a
                                               handoff node
recheck_account_existence     60               Cache timeout in seconds to
                                               send memcached for account
                                               existence
recheck_container_existence   60               Cache timeout in seconds to
                                               send memcached for container
                                               existence
object_chunk_size             65536            Chunk size to read from
                                               object servers
client_chunk_size             65536            Chunk size to read from
                                               clients
memcache_servers              127.0.0.1:11211  Comma separated list of
                                               memcached servers ip:port
node_timeout                  10               Request timeout to external
                                               services
client_timeout                60               Timeout to read one chunk
                                               from a client
conn_timeout                  0.5              Connection timeout to
                                               external services
error_suppression_interval    60               Time in seconds that must
                                               elapse since the last error
                                               for a node to be considered
                                               no longer error limited
error_suppression_limit       10               Error count to consider a
                                               node error limited
allow_account_management      false            Whether account PUTs and DELETEs
                                               are even callable
object_post_as_copy           true             Set object_post_as_copy = false
                                               to turn on fast posts where only
                                               the metadata changes are stored
                                               anew and the original data file
                                               is kept in place. This makes for
                                               quicker posts; but since the
                                               container metadata isn't updated
                                               in this mode, features like
                                               container sync won't be able to
                                               sync posts.
account_autocreate            false            If set to 'true' authorized
                                               accounts that do not yet exist
                                               within the Swift cluster will
                                               be automatically created.
max_containers_per_account    0                If set to a positive value,
                                               trying to create a container
                                               when the account already has at
                                               least this maximum containers
                                               will result in a 403 Forbidden.
                                               Note: This is a soft limit,
                                               meaning a user might exceed the
                                               cap for
                                               recheck_account_existence before
                                               the 403s kick in.
max_containers_whitelist                       This is a comma separated list
                                               of account names that ignore
                                               the max_containers_per_account
                                               cap.
rate_limit_after_segment      10               Rate limit the download of
                                               large object segments after
                                               this segment is downloaded.
rate_limit_segments_per_sec   1                Rate limit large object
                                               downloads at this rate.
============================  ===============  =============================

[tempauth]

=====================  =============================== =======================
Option                 Default                         Description
---------------------  ------------------------------- -----------------------
use                                                    Entry point for
                                                       paste.deploy to use for
                                                       auth. To use tempauth
                                                       set to:
                                                       `egg:swift#tempauth`
set log_name           tempauth                        Label used when logging
set log_facility       LOG_LOCAL0                      Syslog log facility
set log_level          INFO                            Log level
set log_headers        True                            If True, log headers in
                                                       each request
reseller_prefix        AUTH                            The naming scope for the
                                                       auth service. Swift
                                                       storage accounts and
                                                       auth tokens will begin
                                                       with this prefix.
auth_prefix            /auth/                          The HTTP request path
                                                       prefix for the auth
                                                       service. Swift itself
                                                       reserves anything
                                                       beginning with the
                                                       letter `v`.
token_life             86400                           The number of seconds a
                                                       token is valid.
storage_url_scheme     default                         Scheme to return with
                                                       storage urls: http,
                                                       https, or default
                                                       (chooses based on what
                                                       the server is running
                                                       as) This can be useful
                                                       with an SSL load
                                                       balancer in front of a
                                                       non-SSL server.
=====================  =============================== =======================

Additionally, you need to list all the accounts/users you want here. The format
is::

    user_<account>_<user> = <key> [group] [group] [...] [storage_url]

or if you want to be able to include underscores in the ``<account>`` or
``<user>`` portions, you can base64 encode them (with *no* equal signs) in a
line like this::

    user64_<account_b64>_<user_b64> = <key> [group] [group] [...] [storage_url]

There are special groups of::

    .reseller_admin = can do anything to any account for this auth
    .admin = can do anything within the account

If neither of these groups are specified, the user can only access containers
that have been explicitly allowed for them by a .admin or .reseller_admin.

The trailing optional storage_url allows you to specify an alternate url to
hand back to the user upon authentication. If not specified, this defaults to::

    $HOST/v1/<reseller_prefix>_<account>

Where $HOST will do its best to resolve to what the requester would need to use
to reach this host, <reseller_prefix> is from this section, and <account> is
from the user_<account>_<user> name. Note that $HOST cannot possibly handle
when you have a load balancer in front of it that does https while TempAuth
itself runs with http; in such a case, you'll have to specify the
storage_url_scheme configuration value as an override.

Here are example entries, required for running the tests::

    user_admin_admin = admin .admin .reseller_admin
    user_test_tester = testing .admin
    user_test2_tester2 = testing2 .admin
    user_test_tester3 = testing3

    # account "test_y" and user "tester_y" (note the lack of padding = chars)
    user64_dGVzdF95_dGVzdGVyX3k = testing4 .admin

------------------------
Memcached Considerations
------------------------

Several of the Services rely on Memcached for caching certain types of
lookups, such as auth tokens, and container/account existence.  Swift does
not do any caching of actual object data.  Memcached should be able to run
on any servers that have available RAM and CPU.  At Rackspace, we run
Memcached on the proxy servers.  The `memcache_servers` config option
in the `proxy-server.conf` should contain all memcached servers.

-----------
System Time
-----------

Time may be relative but it is relatively important for Swift!  Swift uses
timestamps to determine which is the most recent version of an object.
It is very important for the system time on each server in the cluster to
by synced as closely as possible (more so for the proxy server, but in general
it is a good idea for all the servers).  At Rackspace, we use NTP with a local
NTP server to ensure that the system times are as close as possible.  This
should also be monitored to ensure that the times do not vary too much.

----------------------
General Service Tuning
----------------------

Most services support either a worker or concurrency value in the settings.
This allows the services to make effective use of the cores available. A good
starting point to set the concurrency level for the proxy and storage services
to 2 times the number of cores available. If more than one service is
sharing a server, then some experimentation may be needed to find the best
balance.

At Rackspace, our Proxy servers have dual quad core processors, giving us 8
cores. Our testing has shown 16 workers to be a pretty good balance when
saturating a 10g network and gives good CPU utilization.

Our Storage servers all run together on the same servers. These servers have
dual quad core processors, for 8 cores total. We run the Account, Container,
and Object servers with 8 workers each. Most of the background jobs are run
at a concurrency of 1, with the exception of the replicators which are run at
a concurrency of 2.

The above configuration setting should be taken as suggestions and testing
of configuration settings should be done to ensure best utilization of CPU,
network connectivity, and disk I/O.

-------------------------
Filesystem Considerations
-------------------------

Swift is designed to be mostly filesystem agnostic--the only requirement
being that the filesystem supports extended attributes (xattrs). After
thorough testing with our use cases and hardware configurations, XFS was
the best all-around choice. If you decide to use a filesystem other than
XFS, we highly recommend thorough testing.

If you are using XFS, some settings that can dramatically impact
performance. We recommend the following when creating the XFS
partition::

    mkfs.xfs -i size=1024 -f /dev/sda1

Setting the inode size is important, as XFS stores xattr data in the inode.
If the metadata is too large to fit in the inode, a new extent is created,
which can cause quite a performance problem. Upping the inode size to 1024
bytes provides enough room to write the default metadata, plus a little
headroom. We do not recommend running Swift on RAID, but if you are using
RAID it is also important to make sure that the proper sunit and swidth
settings get set so that XFS can make most efficient use of the RAID array.

We also recommend the following example mount options when using XFS::

    mount -t xfs -o noatime,nodiratime,nobarrier,logbufs=8 /dev/sda1 /srv/node/sda

For a standard swift install, all data drives are mounted directly under
/srv/node (as can be seen in the above example of mounting /def/sda1 as
/srv/node/sda). If you choose to mount the drives in another directory,
be sure to set the `devices` config option in all of the server configs to
point to the correct directory.

Swift uses system calls to reserve space for new objects being written into
the system. If your filesystem does not support `fallocate()` or
`posix_fallocate()`, be sure to set the `disable_fallocate = true` config
parameter in account, container, and object server configs.

---------------------
General System Tuning
---------------------

Rackspace currently runs Swift on Ubuntu Server 10.04, and the following
changes have been found to be useful for our use cases.

The following settings should be in `/etc/sysctl.conf`::

    # disable TIME_WAIT.. wait..
    net.ipv4.tcp_tw_recycle=1
    net.ipv4.tcp_tw_reuse=1

    # disable syn cookies
    net.ipv4.tcp_syncookies = 0

    # double amount of allowed conntrack
    net.ipv4.netfilter.ip_conntrack_max = 262144

To load the updated sysctl settings, run ``sudo sysctl -p``

A note about changing the TIME_WAIT values.  By default the OS will hold
a port open for 60 seconds to ensure that any remaining packets can be
received.  During high usage, and with the number of connections that are
created, it is easy to run out of ports.  We can change this since we are
in control of the network.  If you are not in control of the network, or
do not expect high loads, then you may not want to adjust those values.

----------------------
Logging Considerations
----------------------

Swift is set up to log directly to syslog. Every service can be configured
with the `log_facility` option to set the syslog log facility destination.
We recommended using syslog-ng to route the logs to specific log
files locally on the server and also to remote log collecting servers.
Additionally, custom log handlers can be used via the custom_log_handlers
setting.
