Hello experts,
I've had a lingering question for some time: when I
use "zpool iostat -v" the values do not quite sum up.
In the example below with a raidz2 array made of 6
drives:
* the reported 33K of writes are less than two disks'
workload at this time (at 17.9K each), overall
disks writes are 107.4K = 325% of 33K.
* write ops sum up to 18 = 225% of 8 ops to the pool;
* read MB on dirves is 66.2M = 190% of 34.8M read
from pool;
* read ops on drives sum up to 2014, but pool IOs
are reported as 804 (disk work is 250% higher);
Neither difference is the same, and neither matches
the 150% (50% increase) I had expected from 2 parity
drives with 4 data drives worth of data.
Per-disk values are consistent with "iostat -Xn"
output. So I think that accounting of pool/vdev IO
is lying somewhere...
I'm curious: What's up? ;)
capacity operations bandwidth
pool alloc free read write read write
---------- ----- ----- ----- ----- ----- -----
pool 9.53T 1.34T 804 8 34.8M 33.0K
raidz2 9.53T 1.34T 804 8 34.8M 33.0K
c7t0d0 - - 296 3 11.9M 17.9K
c7t1d0 - - 338 3 10.7M 17.9K
c7t2d0 - - 367 3 10.4M 17.9K
c7t3d0 - - 333 3 12.0M 17.9K
c7t4d0 - - 340 3 10.7M 17.9K
c7t5d0 - - 340 3 10.5M 17.9K
cache - - - - - -
c4t1d0p2 230M 15.8G 0 0 0 0
c4t1d0p3 231M 15.5G 0 0 0 0
---------- ----- ----- ----- ----- ----- -----
Sometimes values are even more weird, i.e. here pool
reads are even less than one component drive's workload,
not to mention all six of them:
capacity operations bandwidth
pool alloc free read write read write
---------- ----- ----- ----- ----- ----- -----
pool 9.53T 1.34T 404 0 4.41M 0
raidz2 9.53T 1.34T 404 0 4.41M 0
c7t0d0 - - 115 0 4.25M 0
c7t1d0 - - 141 0 4.50M 0
c7t2d0 - - 133 0 4.41M 0
c7t3d0 - - 133 0 4.22M 0
c7t4d0 - - 138 0 4.47M 0
c7t5d0 - - 141 0 4.45M 0
cache - - - - - -
c4t1d0p2 230M 15.8G 0 0 0 0
c4t1d0p3 231M 15.5G 0 0 0 0
---------- ----- ----- ----- ----- ----- -----
capacity operations bandwidth
pool alloc free read write read write
---------- ----- ----- ----- ----- ----- -----
pool 9.53T 1.34T 371 7 3.74M 29.3K
raidz2 9.53T 1.34T 371 7 3.74M 29.3K
c7t0d0 - - 115 2 3.62M 16.5K
c7t1d0 - - 132 2 3.70M 15.3K
c7t2d0 - - 137 3 3.66M 15.3K
c7t3d0 - - 138 3 3.55M 15.3K
c7t4d0 - - 145 3 3.69M 16.5K
c7t5d0 - - 138 2 3.69M 16.5K
cache - - - - - -
c4t1d0p2 230M 15.8G 0 0 0 0
c4t1d0p3 231M 15.5G 0 0 0 0
---------- ----- ----- ----- ----- ----- -----
Thanks,
//Jim Klimov
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