Thank you Bill and Richard for your responses.
In sync_speed_max, I had already set it to 250000 (250MB/sec). For
sync_speed_min, I have 249900 set. My rational behind doing this was to
"force" it to go as fast as it can. Any problem with this?
However, adjusting stripe_cache_size did improve performance. It was
256 at first, and my sync rate was 28MB/sec. When I increased it to
4096, my sync rate jumped to 38MB/sec. Then I increased it to 16384,
and it jumped again to 40MB/sec. Increasing stripe_cache_size above
that did not seem to have any effect.
My question then is, how do I set the stripe_cache_size at the time of
md creation? I would rather set it then, as opposed to having to echo
stripe_cache_size variable with a new setting. In other words, where is
this default value of 256 coming from? Thanks all!!
-Thomas
-----Original Message-----
From: Bill Davidsen <davidsen@xxxxxxx>
To: thomas62186218@xxxxxxx
Cc: linux-raid@xxxxxxxxxxxxxxx
Sent: Mon, 2 Jun 2008 5:35 am
Subject: Re: Software RAID 6 initial sync very slow
thomas62186218@xxxxxxx wrote:
Hi all,
I am debating between hardware or software RAID for a
high-performance
Linux storage server. One area of concern in my initial mdadm tests
concerns sync speed. My setup is as follows:
Linux Fedora 7 x64
12 x 1TB Hitachi 1TB SATAII drives connected via LSI SAS3801E PCIe
HBA
Dual 2.5GHz quad-core Xeon
8GB RAM
My first test was to create a RAID 6 md device, 128K chunk, with all
12 drives. The sync is currently underway at a very slow 30MB/sec,
with mdadm estimating this as a 9hr process. With an Adaptec 5805
RAID
card tested, I performed the RAID 6 initial sync with the same 12
drives in just under 5 hours. Meanwhile, our total CPU usage during
mdadm syncing is at 5%, so there's plenty of CPU not being used.
Why is the sync so slow? This concerns me not only because initial
sync time is important, but because this may be indicative of slow
sync times in the event of a drive failure.
Two things will limit this, chunk size and max speed set in the
/sys/block/mdNN/md/sync_speed_max setting. What you are seeing does
sound slow.
--
Bill Davidsen <davidsen@xxxxxxx>
"Woe unto the statesman who makes war without a reason that will still
be valid when the war is over..." Otto von Bismark
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