Re: Possible to change chunk size on RAID-1 without re-init or destructive result?

[Stan Hoeppner <stan@hardwarefreak.com>]

On 3/31/2013 12:56 PM, Mark Knecht wrote:
> On Sun, Mar 31, 2013 at 10:41 AM, Stan Hoeppner <stan@hardwarefreak.com> wrote:
>> On 3/31/2013 12:15 PM, Mark Knecht wrote:
> <SNIP>
>>>
>>> Hopefully that gives you enough info to suggest a direction.
>>
>> These applications append small data slowly over a long period of time,
>> which usually means fragmentation.  Thus there's not much to optimize at
>> the chunk/stripe level, other than keeping chunk size small to spread
>> random reads over all platters.  You currently have a 16KB chunk, IIRC,
>> which is about as good as you'll get for this workload.  Given your
>> applications' low write throughput chunk/strip really doesn't matter.
>>
>> --
>> Stan
>>
> 
> OK, I cannot argue with your conclusions and will stick with 16K for now.
> 
> Presumably if any improvement is to be made here its getting
> everything onto a single partition instead of multiple RAIDs on the
> same drives which then reduces the physical overhead (moving heads to
> different partitions) and allows the md software to do the heavy
> lifting?

Your write IO rate appears to be so low that it really makes no
difference.  I'd guess you could run all of this from a single fast disk
drive (10/15K or SSD) without skipping a beat.

-- 
Stan