Re: Optimize RAID0 for max IOPS?

From: "Stefan /*St0fF*/ Hübner" <stefan.huebner@stud.tu-ilmenau.de>
To: Wolfgang Denk <wd@denx.de>
Cc: linux-raid@vger.kernel.org
Subject: Re: Optimize RAID0 for max IOPS?
Date: Wed, 19 Jan 2011 00:15:50 +0100	[thread overview]
Message-ID: <4D361F26.3060507@stud.tu-ilmenau.de> (raw)
In-Reply-To: <20110118210112.D13A236C@gemini.denx.de>

Hi,

[in German:] Schätzelein, Dein Problem sind die Platten, nicht der
Controller.

[in English:] Dude, the disks are your bottleneck.

On a 4-disk RAID0 software RAID can only outspeed this 3ware Controller
with a really really fast processor.  The limiting factor is the disk's
access time.  If SSDs are too expensive, then your actual performance is
the max you'll get (maybe to replace the HWRAID controller might give a
little speed-up, but not very much).

All the best,
Stefan

Am 18.01.2011 22:01, schrieb Wolfgang Denk:
> Hi,
> 
> I'm going to replace a h/w based RAID system (3ware 9650SE) by a plain
> s/w RAID0, because the existing system appears to be seriously limited
> in terms of numbers of I/O operations per second.
> 
> Our workload is mixed read / write (something between 80% read / 20%
> write and 50% / 50%), consisting of a very large number of usually
> very small files.
> 
> There may be 20...50 millions of files, or more. 65% of the files are
> smaller than 4 kB; 80% are smaller than 8 kB; 90% are smaller than 16
> kB; 98.4% are smaller than 64 kB.
> 
> I will have 4 x 1 TB disks for this setup.
> 
> The plan is to build a RAID0 from the 4 devices, create a physical
> volume and a volume group on the resulting /dev/md?, then create 2 or
> 3 logical volumes that will be used as XFS file systems.
> 
> My goal is to optimize for maximum number of I/O operations per
> second. [I am aware that using SSDs would be a nice thing, but that
> would be too expensive.]
> 
> Is this a reasonable approach for such a task?
> 
> Should I do anything different to acchive maximum performance?
> 
> What are the tunables in this setup?  [It seems the usual recipies are
> more oriented in maximizing the data troughput for large, mostly
> sequential accesses - I figure that things like increasing read-ahead
> etc. will not help me much here?]
> 
> Thanks in advance.
> 
> Best regards,
> 
> Wolfgang Denk
> 

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