Greetings Gentlemen,
I'm currently testing a new setup for a ZFS based storage system with
dedup enabled. The system is setup on OI 148, which seems quite stable
w/ dedup enabled (compared to the OpenSolaris snv_136 build I used
before).
One issue I ran into, however, is quite baffling:
With iozone set to 32 threads, ZFS's ARC seems to consume all available
memory, making the system completely unresponsive (no SSH or console
access).
This happens (repeatably) during one of the READ tests, usually in
iozone's random read test. The WRITE tests work perfectly fine (and
blazingly fast).
The system has 12G RAM. It does not matter whether a reasonably fast
L2ARC is added to the pool.
The only thing that seems to help is setting 'primarycache=metadata' for
the ZFS in question, which does not seem like a desirable configuration.
I have also tried setting the zfs_arc_max property to 0x80000000 (2G)
in /etc/system. This helps a little (it won't lock up quite as quickly),
but at some point, it will still eat up all memory it can get.
IOzone command line:
/usr/benchmarks/iozone/iozone -R -e -s 1g -t 32 -M -r 16k -F [...]
Primarycache property:
NAME PROPERTY VALUE SOURCE
somepool primarycache all local
rpool/swap primarycache metadata local
./arcstat.pl (last few lines before the system locks up):
Time read miss miss% dmis dm% pmis pm% mmis mm% arcsz c
15:56:34 121K 247 0 243 0 4 0 178 1 151M 402M
15:56:35 0 0 0 0 0 0 0 0 0 137M 402M
15:56:36 14K 25 0 25 0 0 0 24 0 265M 402M
15:56:37 381K 575 0 575 0 0 0 574 1 4G 402M
15:56:38 362K 706 0 706 0 0 0 706 1 9G 402M
15:56:39 153K 364 0 306 0 58 18 362 2 11G 402M
zpool list 3 (last output before the system locks up):
somepool 2.72T 9.53M 2.72T 0% 34466.62x ONLINE -
rpool 37G 8.37G 28.6G 22% 1.00x ONLINE -
Is this a known issue with the ARC? Is there anything else I can do
about it?
Also, does anyone have an idea what's actually in the ARC when the
system locks up?
In 'zpool list' output, you can see that only 9.53M on the zpool is in
use, with a dedup rate of 34466.62x. So what's there to cache?
I realize that this test does not reflect a situation that is likely to
occur in a production environment, but I'd still be happy about any
helpful comments.
-- Clemens
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