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Re: relationship of nested stripe sizes, was: Question regarding XFS on

To: stan@xxxxxxxxxxxxxxxxx
Subject: Re: relationship of nested stripe sizes, was: Question regarding XFS on LVM over hardware RAID.
From: Chris Murphy <lists@xxxxxxxxxxxxxxxxx>
Date: Sat, 1 Feb 2014 13:55:16 -0700
Cc: xfs <xfs@xxxxxxxxxxx>
Delivered-to: xfs@xxxxxxxxxxx
In-reply-to: <52ED4143.6090303@xxxxxxxxxxxxxxxxx>
References: <7A732267-B34F-4286-9B49-3AF8767C0B89@xxxxxxxxxxxxxxxxx> <52ED4143.6090303@xxxxxxxxxxxxxxxxx>
On Feb 1, 2014, at 11:47 AM, Stan Hoeppner <stan@xxxxxxxxxxxxxxxxx> wrote:

> On 1/31/2014 12:35 AM, Chris Murphy wrote:
>> Hopefully this is an acceptable way to avoid thread jacking, by
>> renaming the  subject…
>> 
>> On Jan 30, 2014, at 10:58 PM, Stan Hoeppner <stan@xxxxxxxxxxxxxxxxx>
>> wrote:
>>> 
>>> RAID60 is a nested RAID level just like RAID10 and RAID50.  It is
>>> a stripe, or RAID0, across multiple primary array types, RAID6 in
>>> this case.  The stripe width of each 'inner' RAID6 becomes the
>>> stripe unit of the 'outer' RAID0 array:
>>> 
>>> RAID6 geometry       128KB * 12 = 1536KB RAID0 geometry  1536KB * 3  =
>>> 4608KB
>> 
>> My question is on this particular point. If this were hardware raid6,
>> but I wanted to then stripe using md raid0, using the numbers above
>> would I choose a raid0 chunk size of 1536KB? How critical is this
>> value for, e.g. only large streaming read/write workloads? If it were
>> smaller, say 256KB or even 32KB, would there be a significant
>> performance consequence?
> 
> You say 'if it were smaller...256/32KB'.  What is "it" referencing?

it = chunk size for md raid0. 

So chunk size 128KB * 12 disks, hardware raid6. Chunk size 32KB [1] striping 
the raid6's with md raid0.


Chris Murphy

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