I'm using a FC flash drive as a cache device to one of my pools:
zpool add pool-name cache device-name
and I'm running random IO tests to assess performance on a
snv-78 x86 system
I have a set of threads each doing random reads to about 25% of
its own, previously written, large file ... a test run will read in
about 20GB on a server with 2GB of RAM
using zpool iostat, I can see that the SSD device is being used
aggressively, and each time I run my random read test I find
better performance than the previous execution ... I also see my
SSD drive filling up more and more between runs
this behavior is what I expect, and the performance improvements
I see are quite good (4X improvement over 5 runs), but I'm getting
hung from time to time
after several successful runs of my test application, some run of
my test will be running fine, but at some point before it finishes,
I see that all IO to the pool has stopped, and, while I still can use
the system for other things, most operations that involve the pool
will also hang (e.g. a wc on a pool based file will hang)
any of these hung processes seem to sleep in the kernel
at an uninterruptible level, and will not die on a kill -9 attempt
any attempt to shutdown will hang, and the only way I can recover
is to use the reboot -qnd command (I think that the -d option
in the key since it keeps the system from trying to sync before
reboot)
when I reboot, everything is fine again and I can continue testing
until I run into this problem again ... does anyone have any thoughts
on this issue ? ... thanks, Bill
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