Pool Functions
Pool functions provide methods to determine attributes of pools in a PixStor Filesystem.
CLib’s Pool Functions provide faster operation than the equivalent PixStor Python API arcapix.fs.gpfs.pool.Pool.
These methods do not require root permission
Description
statfspool_result struct
The statfspool_result struct returned by statfspool() has the following fields
f_blocks # total data blocks in pool
f_bfree # free blocks in pool
f_bavail # free blocks avail to non-superuser
f_mblocks # total metadata blocks in pool
f_mfree # free blocks avail for system metadata
f_bsize # optimal storage pool block size
f_files # total file nodes assigned to pool
f_poolid # storage pool id
f_fsize # fundamental file system block size
f_usage # data and/or metadata stored in pool
f_replica # replica
f_bgf # block group factor
f_wad # write affinity depth
f_allowWriteAffinity # allow write affinity depth. 1 means yes
f_nextid # id of the next pool in the filesystem or -1 if no more pools
All fields are of type int.
Note
Fields f_replica, f_bgf, f_wad, and f_allowWriteAffinity are new in 4.1.1 file system code.
For earlier versions of PixStor file system code, these fields will all have value 0
- arcapix.fs.gpfs.clib.pool.getpoolname(pathname, gpfs_pool_t poolId)
Retrieves the name of the storage pool.
- arcapix.fs.gpfs.clib.pool.statfspool(pathname, gpfs_pool_t poolId=0, int nPools=0)
Obtain status information about the storage pools.
Hint
These methods specify which filesystem to use by providing a path to some file in the filesystem. You can get the mountpoint for a named filesystem by using Filesystem Snapshot Identifiers methods
>>> from arcapix.fs.gpfs.clib.fssnap import get_fssnaphandle_by_name, get_pathname_from_fssnaphandle
>>>
>>> path = get_pathname_from_fssnaphandle(get_fssnaphandle_by_name('mmfs1'))
>>> pools = statfspool(path)
Examples
List names of pools in a filesystem
>>> for pool in statfspool('/mmfs1'):
... print(getpoolname('/mmfs1', pool.f_poolid))
...
system
sas1
sata1
sata2
Get a pool by id
>>> # REMEMBER statfspool returns a list
>>> pool = statfspool('/mmfs1', poolId=65538, nPools=1)[0]
>>> pool.f_usage & U_DATA != 0 # does the pool hold data?
True
>>> pool.f_usage & U_METADATA != 0 # does the pool hold metadata?
False
Find a pool by name
We could fetch stats for all pools like the example above, however this will load data for all pools into memory. If the filesystem has a lot of pools, this may not be desirable. This example shows iterating over pools, loading only one at a time.
>>> pool = statfspool('/mmfs1', 0, 1)[0] # get first pool
>>>
>>> while pool.f_nextid != -1: # -1 means no next pool
...
... # for this example we're looking for 'sata1'
... if getpoolname('/mmfs1', pool.f_poolid) == 'sata1':
... break
...
... # get next pool
... pool = statfspool('/mmfs1', pool.f_nextid, 1)[0]
...
... else:
... raise Exception("pool 'sata1' wasn't found")
...
>>> print(pool.f_poolid)
65538
Check available space in data pools
>>> for pool in statfspool('/mmfs1'):
...
... if pool.f_usage & U_DATA == 0:
... # pool doesn't hold data (metadata only)
... continue
...
... name = getpoolname('/mmfs1', pool.f_poolid)
...
... # free blocks * block size = free bytes
... free_kb = pool.f_bfree * pool.f_bsize / 1024
...
... # free block / total blocks
... free_pct = 100 * pool.f_bfree / pool.f_blocks
...
... print("%s\t%d\t%10d KB (%3d %%)" % (name, pool.f_poolid, free_kb, free_pct))
...
sas1 65537 10412032 KB ( 99 %)
sata1 65538 9162752 KB ( 87 %)
sata2 65539 5169152 KB ( 98 %)