Hi,
If after it decreases in size it stays there it might be similar to:
7111576 arc shrinks in the absence of memory pressure
Also, see document:
ZFS ARC can shrink down without memory pressure result in slow
performance [ID 1404581.1]
Specifically, check if arc_no_grow is set to 1 after the cache size is
decreased, and if it stays that way.
The fix is in one of the SRUs and I think it should be in 11.1
I don't know if it was fixed in Illumos or even if Illumos was affected by
this at all.
--
Robert Milkowski
http://milek.blogspot.com
> -----Original Message-----
> From: zfs-discuss-boun...@opensolaris.org [mailto:zfs-discuss-
> boun...@opensolaris.org] On Behalf Of Chris Nagele
> Sent: 20 October 2012 18:47
> To: zfs-discuss@opensolaris.org
> Subject: [zfs-discuss] ARC de-allocation with large ram
>
> Hi. We're running OmniOS as a ZFS storage server. For some reason, our
> arc cache will grow to a certain point, then suddenly drops. I used
> arcstat to catch it in action, but I was not able to capture what else
> was going on in the system at the time. I'll do that next.
>
> read hits miss hit% l2read l2hits l2miss l2hit% arcsz l2size
> 166 166 0 100 0 0 0 0 85G 225G
> 5.9K 5.9K 0 100 0 0 0 0 85G 225G
> 755 715 40 94 40 0 40 0 84G 225G
> 17K 17K 0 100 0 0 0 0 67G 225G
> 409 395 14 96 14 0 14 0 49G 225G
> 388 364 24 93 24 0 24 0 41G 225G
> 37K 37K 20 99 20 6 14 30 40G 225G
>
> For reference, it's a 12TB pool with 512GB SSD L2 ARC and 198GB RAM.
> We have nothing else running on the system except NFS. We are also not
> using dedupe. Here is the output of memstat at one point:
>
> # echo ::memstat | mdb -k
> Page Summary Pages MB %Tot
> ------------ ---------------- ---------------- ----
> Kernel 19061902 74460 38%
> ZFS File Data 28237282 110301 56%
> Anon 43112 168 0%
> Exec and libs 1522 5 0%
> Page cache 13509 52 0%
> Free (cachelist) 6366 24 0%
> Free (freelist) 2958527 11556 6%
>
> Total 50322220 196571
> Physical 50322219 196571
>
> According to "prstat -s rss" nothing else is consuming the memory.
>
> 592 root 33M 26M sleep 59 0 0:00:33 0.0% fmd/27
> 12 root 13M 11M sleep 59 0 0:00:08 0.0%
> svc.configd/21
> 641 root 12M 11M sleep 59 0 0:04:48 0.0% snmpd/1
> 10 root 14M 10M sleep 59 0 0:00:03 0.0%
> svc.startd/16
> 342 root 12M 9084K sleep 59 0 0:00:15 0.0% hald/5
> 321 root 14M 8652K sleep 59 0 0:03:00 0.0% nscd/52
>
> So far I can't figure out what could be causing this. The only other
> thing I can think of is that we have a bunch of zfs send/receive
> operations going on as backups across 10 datasets in the pool. I am
> not sure how snapshots and send/receive affect the arc. Does anyone
> else have any ideas?
>
> Thanks,
> Chris
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