From: Michael Tokarev <mjt@tls.msk.ru>
To: linux-raid@vger.kernel.org
Subject: Re: raid6 + caviar black + mpt2sas horrific performance
Date: Thu, 31 Mar 2011 11:11:48 +0400 [thread overview]
Message-ID: <4D942934.3030605@msgid.tls.msk.ru> (raw)
In-Reply-To: <20110330152011.GA6863@apartia.fr>
30.03.2011 19:20, Louis-David Mitterrand wrote:
[]
> /dev/mapper/cmd1 / xfs defaults,inode64,delaylog,logbsize=262144 0 0
> /dev/mapper/cmd1 / xfs defaults,inode64,delaylog,logbsize=262144 0 0
>
>> [root@vault t]# dd if=/dev/zero of=/backup/t/big.file bs=32k count=32000
>
> 1048576000 octets (1,0 GB) copiés, 0,870001 s, 1,2 GB/s
> 1048576000 bytes (1.0 GB) copied, 9.11934 s, 115 MB/s
Are you sure your LVM volumes are aligned to raid stripe size correctly?
Proper alignment for raid levels with parity is _critical_, and with
8-drive raid6 you'll have 6 data disks in eash stripe, but since LVM
can only align volumes to a power of two, you'll have 2 unaligned
volumes after each aligned... Verify that the volume starts at the
raid stripe boundary, maybe create new volume and recheck -- there
should be quite dramatic speed difference like the above when you
change from aligned to misaligned.
/mjt
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next prev parent reply other threads:[~2011-03-31 7:11 UTC|newest]
Thread overview: 11+ messages / expand[flat|nested] mbox.gz Atom feed top
2011-03-30 8:08 raid6 + caviar black + mpt2sas horrific performance Louis-David Mitterrand
2011-03-30 13:20 ` Stan Hoeppner
2011-03-30 13:42 ` Robin Hill
2011-03-30 13:46 ` Joe Landman
2011-03-30 15:20 ` Louis-David Mitterrand
2011-03-30 16:12 ` Joe Landman
2011-03-31 9:32 ` Louis-David Mitterrand
2011-04-19 11:04 ` Louis-David Mitterrand
2011-03-30 19:26 ` Iordan Iordanov
2011-03-31 7:11 ` Michael Tokarev [this message]
2011-03-31 9:35 ` Louis-David Mitterrand
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