Ross Schaulis wrote:
(Please reply to me directly as I am not on the ZFS alias)
IHAC running BEA WebLogic on a T2000 with ZFS.
Here's what he's telling me.....
- He found himself running out of memory on the T2000 (16GB)
In most similar cases, it is a misunderstanding of how memory is
used on a virtual memory OS such as Solaris. It is insufficient to
determine a memory shortfall by observing only the amount of
free memory reported by vmstat. There are quite a few well-written
books, articles, and blogs which will help you determine if your
workload suffer from a memory shortfall.
- He rebooted his T2000 and got all his memory back
- He ran his system for a while and then did a vmstat and showed he
had 10G available. He copied what should have been ~ 5Gig to disk and
immediately re-ran vmstat and it showed he only had 2Gig memory left!!!
Free memory reported by vmstat should drop to around the
lotsfree limit, which by default will be around 512 kBytes (!)
Indeed, there is little need to force caches to shrink until the
demand reaches that sort of level.
For ZFS-specific accounting, the arcstat program will help show
how the Adaptive Replacement Cache (ARC) is being adjusted
over time. Later versions of OpenSolaris have even more ARC
instrumentation available.
-- richard
My guess is that ZFS is using the system memory for cache and is not
giving it back? OR maybe ZFS will give it back when asked? Are there
better commands to run to see actual memory available? Is there a way
to cap the amount of memory being used for cache by ZFS? Or better yet
is there a tuning guide I can give to my customer to help him better
understand and run his ZFS environment? (I think there used to be an
evil tuning guide...but I have been unable to find it)
RS
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