- Openstack-swift ring builder
The swift-ring-builder utility is used to create, search and manipulate the
swift storage ring. The ring-builder assigns partitions to devices and writes
an optimized Python structure to a gzipped, pickled file on disk for shipping
out to the servers. The server processes just check the modification time of
the file occasionally and reload their in-memory copies of the ring structure
as needed. Because of how the ring-builder manages changes to the ring, using
a slightly older ring usually just means one of the three replicas for a
subset of the partitions will be incorrect, which can be easily worked around.
The ring-builder also keeps its own builder file with the ring information and
additional data required to build future rings. It is very important to keep
multiple backup copies of these builder files. One option is to copy the
builder files out to every server while copying the ring files themselves.
Another is to upload the builder files into the cluster itself. Complete loss
of a builder file will mean creating a new ring from scratch, nearly all
partitions will end up assigned to different devices, and therefore nearly all
data stored will have to be replicated to new locations. So, recovery from a
builder file loss is possible, but data will definitely be unreachable for an
If invoked as 'swift-ring-builder-safe' the directory containing the builder
file provided will be locked (via a .lock file in the files parent directory).
This provides a basic safe guard against multiple instances of the
swift-ring-builder (or other utilities that observe this lock) from attempting
to write to or read the builder/ring files while operations are in progress.
This can be useful in environments where ring management has been automated
but the operator still needs to interact with the rings manually.
- Can be of the form:
- Any part is optional, but you must include at least one, examples:
- d74 Matches the device id 74
- z1 Matches devices in zone 1
- z1-22.214.171.124 Matches devices in zone 1 with the ip 126.96.36.199
- 188.8.131.52 Matches devices in any zone with the ip 184.108.40.206
- z1:5678 Matches devices in zone 1 using port 5678
- :5678 Matches devices that use port 5678
- /sdb1 Matches devices with the device name sdb1
- _shiny Matches devices with shiny in the meta data
- _'snet: 220.127.116.11' Matches devices with snet: 18.104.22.168 in the meta data
- [::1] Matches devices in any zone with the ip ::1
- z1-[::1]:5678 Matches devices in zone 1 with ip ::1 and port 5678
Most specific example:
- All items require their single character prefix except the ip, in which
case the - is optional unless the device id or zone is also included.
Shows information about the ring and the devices
- search <search-value>
Shows information about matching devices.
- add -r <region> -z <zone> -i <ip> -p <port>
-d <device_name> -m <meta> -w <weight>
Adds a device to the ring with the given information. No
partitions will be assigned to the new device until after running 'rebalance'.
This is so you can make multiple device changes and rebalance them all just
- create <part_power> <replicas>
Creates <builder_file> with 2^<part_power>
partitions and <replicas>. <min_part_hours> is number of hours to
restrict moving a partition more than once.
- list_parts <search-value> [<search-value>] ..
Returns a 2 column list of all the partitions that are
assigned to any of the devices matching the search values given. The first
column is the assigned partition number and the second column is the number of
device matches for that partition. The list is ordered from most number of
matches to least. If there are a lot of devices to match against, this command
could take a while to run.
Attempts to rebalance the ring by reassigning partitions
that haven't been recently reassigned.
- remove <search-value>
Removes the device(s) from the ring. This should normally
just be used for a device that has failed. For a device you wish to
decommission, it's best to set its weight to 0, wait for it to drain all its
data, then use this remove command. This will not take effect until after
running 'rebalance'. This is so you can make multiple device changes and
rebalance them all just once.
- set_info <search-value>
Resets the device's information. This information isn't
used to assign partitions, so you can use 'write_ring' afterward to rewrite
the current ring with the newer device information. Any of the parts are
optional in the final <ip>:<port>/<device_name>_<meta>
parameter; just give what you want to change. For instance set_info d74
_"snet: 22.214.171.124" would just update the meta data for device id
- set_min_part_hours <hours>
Changes the <min_part_hours> to the given
<hours>. This should be set to however long a full replication/update
cycle takes. We're working on a way to determine this more easily than
- set_weight <search-value> <weight>
Resets the device's weight. No partitions will be
reassigned to or from the device until after running 'rebalance'. This is so
you can make multiple device changes and rebalance them all just once.
Just runs the validation routines on the ring.
Just rewrites the distributable ring file. This is done
automatically after a successful rebalance, so really this is only useful
after one or more 'set_info' calls when no rebalance is needed but you want to
send out the new device information.
add create list_parts rebalance remove search set_info
set_min_part_hours set_weight validate write_ring
0 = ring changed, 1 = ring did not change, 2 = error
More in depth documentation about the swift ring and also Openstack-Swift as a
whole can be found at http://swift.openstack.org/overview_ring.html,