From: NeilBrown <neilb@suse.de>
To: Daniel Pocock <daniel@pocock.com.au>
Cc: linux-raid@vger.kernel.org
Subject: Re: read-ahead for md/lvm combination
Date: Sun, 13 May 2012 07:32:40 +1000 [thread overview]
Message-ID: <20120513073240.2d292ec4@notabene.brown> (raw)
In-Reply-To: <4FAD2866.8070209@pocock.com.au>
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On Fri, 11 May 2012 14:55:34 +0000 Daniel Pocock <daniel@pocock.com.au> wrote:
>
>
> While I was adding the SCTERC settings to my rc.local, I had a look over
> /sbin/blockdev --setra ... settings
>
> I do things like this, for example:
>
> /sbin/blockdev --setra 8192 /dev/mapper/myvg-large_media_files
>
> What about
> - the devices /dev/sd[ab]2
> - the md device, /dev/md2 (which is the PV for LVM) ?
>
> Would it be correct to leave /dev/sd[ab]2 and /dev/md2 at defaults, and
> only specify larger sizes for LVs that need it? Or should I even make
> /dev/sd[ab]2 and /dev/md2 smaller than the default value (256)?
The read-ahead setting is interpreted by the pagecache.
So it only makes sense to set in on a device which is directly mounted or
accessed via /dev/XXX.
On other devices - such as the media device beneath and md array - you can
set the read-ahead to anything or nothing and it will have no effect at all.
NeilBrown
>
>
> Those disks are SATA - but I'm also planning to add in some SSDs and
> RAID1 them with md - they will hold things like source code and home
> directories (to make compiling and NFS home directories faster). Can
> anyone comment on the read ahead config or any other aspect of such a plan?
> --
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prev parent reply other threads:[~2012-05-12 21:32 UTC|newest]
Thread overview: 2+ messages / expand[flat|nested] mbox.gz Atom feed top
2012-05-11 14:55 read-ahead for md/lvm combination Daniel Pocock
2012-05-12 21:32 ` NeilBrown [this message]
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