xfs
[Top] [All Lists]

Re: Performance problem - reads slower than writes

To: Stan Hoeppner <stan@xxxxxxxxxxxxxxxxx>
Subject: Re: Performance problem - reads slower than writes
From: Brian Candler <B.Candler@xxxxxxxxx>
Date: Fri, 3 Feb 2012 22:10:15 +0000
Cc: Christoph Hellwig <hch@xxxxxxxxxxxxx>, xfs@xxxxxxxxxxx
Dkim-signature: v=1; a=rsa-sha1; c=relaxed; d=pobox.com; h=date:from:to :cc:subject:message-id:references:mime-version:content-type :in-reply-to; s=sasl; bh=W7fxEeD5ziCaaXF8XcnLZTw7SF4=; b=wVRCFr9 3yPJS7HgPxr/3EgtSYXjIanZ6Lrd/ceFuNPzkBtK1XdRQIr5RtTviRkeB1eUjR/w 8DNun+KLvGqRw1CqLZRnsNhlGTP8fCHcrvQR5BZkKbmFe34YeXYzy/tn5fm5wQ0R r/OD1fd777Iv4HTjffd1dqRlguAiRiMCWXsA=
Domainkey-signature: a=rsa-sha1; c=nofws; d=pobox.com; h=date:from:to:cc :subject:message-id:references:mime-version:content-type :in-reply-to; q=dns; s=sasl; b=bpQBNK82kGluEFYce+DM2WgDXuq0GT6UQ EVc1tnKQvReWnCtk9Ys8zYR+vOwYno4DcF7MyyF8sOWuafntz/J/Tm5FMdLaKlVe M+Vs4FQ5MHC8P5FpklRheRn4IRtYBKwk8D8GyoUaK+6vJn/TIYZPh3EgQv240FVA k3PkfzgIcI=
In-reply-to: <4F2C38BE.2010002@xxxxxxxxxxxxxxxxx>
References: <20120130220019.GA45782@xxxxxxxx> <20120131020508.GF9090@dastard> <20120131103126.GA46170@xxxxxxxx> <20120131145205.GA6607@xxxxxxxxxxxxx> <20120203115434.GA649@xxxxxxxx> <4F2C38BE.2010002@xxxxxxxxxxxxxxxxx>
User-agent: Mutt/1.5.21 (2010-09-15)
On Fri, Feb 03, 2012 at 01:42:54PM -0600, Stan Hoeppner wrote:
> You've hit the peak read rate of these Hitachi drives.  As others
> pointed out, if you need more read performance than the dozen of these
> you plan to RAID stripe, then you'll need to swap them for units with a
> faster spindle:
> 
> 7.2k   1.21x
>  10k   1.68x
>  15k   2.53x
> 
> or with SSDs, which will yield an order of magnitude increase.  Your
> stated need is 20M 500-800KB files, or 20GB if my math is correct.

Thanks for your suggestion, but unfortunately your maths isn't correct: 20M
x 0.65MB = 13TB.  And that's just one of many possible datasets like this.

I'm aware that I'm working with low-performance drives. This is intentional:
we need low power consumption so we can get lots in a rack, and large
capacity at low cost.

Fortunately our workload will also parallelise easily, and throwing it
across 24 spindles will be fine.  But obviously I want to squeeze the most
performance out of each spindle we have first.  I'm very happy to have found
the bottleneck that was troubling me :-)

Regards,

Brian.

<Prev in Thread] Current Thread [Next in Thread>