Re: MD RAID Bug 7/15/12

["Stefan /*St0fF*/ Hübner" <st0ff.npl@googlemail.com>]

Am 01.10.2012 00:16, schrieb Chris Murphy:
> 
> On Sep 30, 2012, at 3:08 PM, Stefan /*St0fF*/ Hübner wrote:
> 
> 
>> Also off topic: 12 drives would be as "nearly unalignable" as 19 are.
> 
> I'm not sure what you mean by unalignable. A separate question is if a 4K chunks size is a good idea, even with 24 disks, but I'm unsure of the usage and workload.
> 
> 
[...]
By that I mean that optimal alignment has to do with a reasonable chunk
size and an amount of data disks that is/should be a power of two.  If
you made a databases commit chunk size 64k, you'd create maybe a raid6
of 6 drives with a 16k chunk size.  That way you'd spare many many
read-modify-write operations, as on every commit it'd write all 6 disks
once and no rmw would happen.  You'd also have to take care of proper
partition placement.

That probably is what you know as alignment.  I just want to make it
more concious that not only the placement of a data partition goes into
alignment, also the size of a "normal" data packet relative to chunk
size and amount of disks used.

cheers,
stefan

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