On 7/11/2010 3:21 AM, Philippe Schwarz wrote:
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Hi,
i bought a little SSD (OCZ Agility 30GB) and added half to L2ARC and
second half to ZIL:
zpool add zfsda1 log da3s2
zpool add zfsda1 cache da3s1
zpool status
pool: zfsda1
state: ONLINE
scrub: none requested
config:
NAME STATE READ WRITE CKSUM
zfsda1 ONLINE 0 0 0
da1 ONLINE 0 0 0
logs ONLINE 0 0 0
da3s2 ONLINE 0 0 0
cache
da3s1 ONLINE 0 0 0
errors: No known data errors
OK, let's try to burst the write (WC disabled on the Raid controller)
...
Result is ...awful!
A `zpool iostat -v 1` shows:
- - Although the L2ARC (da3s1) is showed separately from the pool, the ZIL
(da3s2) is shown within the pool. Is it the normal behaviour ?
Yes, it's just a quirk of the output format.
- - ZIL seems to be quiet almost all the time and burst sometimes. OK, i
may the normal behaviour of a cache.
capacity operations bandwidth
pool used avail read write read write
- ---------- ----- ----- ----- ----- ----- -----
zfsda1 2.36G 694G 0 176 0 21.8M
da1 2.36G 694G 0 56 0 6.88M
da3s2 128K 15.0G 0 119 0 15.0M
cache - - - - - -
da3s1 3.06G 11.7G 0 0 0 0
- ---------- ----- ----- ----- ----- ----- -----
But, at the end of the copy process (copy a 1GB file from& to the same
pool), the used capacity of the ZIL remains unchanged... Puzzling..
- - And ,last but not least... the copy isn't faster at all!
- -- Without ZIL&L2ARC
time cp /zfsda1/rnd /zfsda1/rn2
real 3m23.297s
- -- With ZIL&L2ARC
time cp /zfsda1/rnd /zfsda1/rn2
real 3m34.847s
Should i call my (dummy) test into question ?
Thanks.
Best regards.
ZIL speeds up synchronous writes only. Operations like 'cp' use async
writes, so ZIL will be of no benefit, since it's not being used.
--
Erik Trimble
Java System Support
Mailstop: usca22-123
Phone: x17195
Santa Clara, CA
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