Greetings learned ZFS geeks & guru’s,
Yet another question comes from my continued ZFS performance testing. This has
to do with zpool iostat, and the strangeness that I do see.
I’ve created an eight (8) disk raidz pool from a Sun 3510 fibre array giving me
a 465G volume.
# zpool create tp raidz c4t600 ... 8 disks worth of zpool
# zfs create tp/pool
# zfs set recordsize=8k tp/pool
# zfs set mountpoint=/pool tp/pool
I then create a 100G data file that is created by sequentially writing 64k
blocks to the test data file. When I then issue a
# zpool iostat -v tp 10
I see the following strange behaviour. I see anywhere from up to 16 iterations
(ie 160 seconds) of the following, where there are only writes to 2 of the 8
disks:
capacity operations bandwidth
pool used avail read write read write
-------------------------------------- ----- ----- ----- ----- ----- -----
testpool 29.7G 514G 0 2.76K 0 22.1M
raidz1 29.7G 514G 0 2.76K 0 22.1M
c4t600C0FF0000000000A74531B659C5C00d0s6 - - 0 0 0
0
c4t600C0FF0000000000A74533F3CF1AD00d0s6 - - 0 0 0
0
c4t600C0FF0000000000A74534C5560FB00d0s6 - - 0 0 0
0
c4t600C0FF0000000000A74535E50E5A400d0s6 - - 0 1.38K 0
2.76M
c4t600C0FF0000000000A74537C1C061500d0s6 - - 0 0 0
0
c4t600C0FF0000000000A745343B08C4B00d0s6 - - 0 0 0
0
c4t600C0FF0000000000A745379CB90B600d0s6 - - 0 0 0
0
c4t600C0FF0000000000A74530237AA9300d0s6 - - 0 1.38K 0
2.76M
-------------------------------------- ----- ----- ----- ----- ----- -----
During these periods, my data file does not grow in size, but then I see writes
to all of the disks like the following:
capacity operations bandwidth
pool used avail read write read write
-------------------------------------- ----- ----- ----- ----- ----- -----
testpool 64.0G 480G 0 1.45K 0 11.6M
raidz1 64.0G 480G 0 1.45K 0 11.6M
c4t600C0FF0000000000A74531B659C5C00d0s6 - - 0 246 0
8.22M
c4t600C0FF0000000000A74533F3CF1AD00d0s6 - - 0 220 0
8.23M
c4t600C0FF0000000000A74534C5560FB00d0s6 - - 0 254 0
8.20M
c4t600C0FF0000000000A74535E50E5A400d0s6 - - 0 740 0
1.45M
c4t600C0FF0000000000A74537C1C061500d0s6 - - 0 299 0
8.21M
c4t600C0FF0000000000A745343B08C4B00d0s6 - - 0 284 0
8.21M
c4t600C0FF0000000000A745379CB90B600d0s6 - - 0 266 0
8.22M
c4t600C0FF0000000000A74530237AA9300d0s6 - - 0 740 0
1.45M
-------------------------------------- ----- ----- ----- ----- ----- -----
And my data file will increase in size, but also notice notice, in the above,
those disks that were being written to before, have a load that is consistent
with the previous example.
For background, the server, and the storage are dedicated solely to this
testing, and there are no other applications being run at this time.
I thought that RaidZ would spread its load across all disks somewhat evenly.
Can someone explain this result? I can consistently reproduce it as well.
Thanks
-Tony
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