From: Richard Elling <[email protected]>
Subject: Re: [OpenIndiana-discuss] Mitigating the performance impact of scrub
To: "Discussion list for OpenIndiana" <[email protected]>
Date: Thursday, September 27, 2012, 1:15 PM
On Sep 27, 2012, at 8:44 AM, Reginald
Beardsley <[email protected]>
wrote:
The only thing google turned up was "stop the scrub if
it impacts performance too badly" which is not really all
that helpful. Or ways to speed up scrubs & resilvers.
On modern ZFS implementations, scrub I/O is throttled to
avoid impacting application I/O
performance. There are some kernel-level tunable parameters
that can be adjusted, but
AFAIK, nobody has done any characterization studies.
In my case, I'd like to be able to run a scrub and have
all the performance hits taken by the scrub process if the
system has other loads. I care that the scrub runs,
but not how fast.
From observed behavior, it appears that the scrub is
consuming too large a share of DRAM (12 GB in this
case). Is that correct and if so, is there a way to
limit the proportion of memory used by the scrub process?
Data is cached in the ARC, but scrub data is placed in the
MRU/LRU side of the ARC
and shouldn't impact the MFU side. In most cases, the memory
usage during a scrub
is not a problem. Have you seen a different behaviour?
-- richard
I'd like to be able to schedule scrubs regularly, but
the present behavior would require predicting when I didn't
want to use the system for work.
Thanks,
Reg
--
illumos Day & ZFS Day, Oct 1-2, 2012 San Fransisco
www.zfsday.com
[email protected]
+1-760-896-4422
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