Hi,
I'm currently testing a Mtron Pro 7500 16GB SLC SSD as a ZIL device and
seeing very poor performance for small file writes via NFS.
Copying a source code directory with around 4000 small files to the ZFS
pool over NFS without the SSD log device yields around 1000 IOPS (pool
of 8 sata shared mirrors).
When adding the SSD as ZIL, performance drops to 50 IOPS!
I can see similarly poor performance when creating a ZFS pool on the SSD
and sharing it via NFS. However copy the files locally on the server
from the sata to the ssd pool only takes a few seconds.
The SSD's specs reveal:
sequential r/w 512B: 83,000/51,000
sequential r/w 4KB: 21,000/13,000
random r/w 512B: 19,000/130
random r/w 4KB: 12,000/130
So it is apparent, that the SSD has really poor random writes.
But I was under the impression, that the ZIL is mostly sequential writes
or was I misinformed here?
Maybe the cache syncs bring the device to it's knees?
Best Regards,
Felix Buenemann
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