Re: Raid 10 chunksize

Scott Carey wrote:
> On 3/25/09 9:28 PM, "Mark Kirkwood" <markir(at)paradise(dot)net(dot)nz> wrote:
>
>
>>
>> Rebuilt with 64K chunksize:
>>
>> transaction type: TPC-B (sort of)
>> scaling factor: 100
>> number of clients: 24
>> number of transactions per client: 12000
>> number of transactions actually processed: 288000/288000
>> tps = 866.512162 (including connections establishing)
>> tps = 866.651320 (excluding connections establishing)
>>
>>
>> So 64K looks quite a bit better. I'll endeavor to try out 256K next week
>> too.
>>
>
> Just go all the way to 1MB, md _really_ likes 1MB chunk sizes for some
> reason. Benchmarks right and left on google show this to be optimal. My
> tests with md raid 0 over hardware raid 10's ended up with that being
> optimal as well.
>
> Greg's notes on aligning partitions to the chunk are key as well.
>
>
Rebuilt with 256K chunksize:

transaction type: TPC-B (sort of)
scaling factor: 100
number of clients: 24
number of transactions per client: 12000
number of transactions actually processed: 288000/288000
tps = 942.852104 (including connections establishing)
tps = 943.019223 (excluding connections establishing)

A noticeable improvement again. I'm not sure that we will have time (or
patience from the system guys that I keep bugging to redo the raid
setup!) to try 1M, but 256K gets us 40% or so improvement over the
original 4K setup - which is quite nice!

Looking on the net for md raid benchmarks, it is not 100% clear to me
that 1M is the overall best - several I found had tested sizes like 64K,
128K, 512K, 1M and concluded that 1M was best - but without testing
256K! whereas others had included ranges <=512K and decided that that
256K was the best. I'd be very interested in seeing your data! (several
years ago I had carried out this type of testing - on a different type
of machine, and for a different database vendor, but found that 256K
seemed to give the overall best result).

The next step is to align the raid 10 partitions, as you and Greg
suggest and see what effect that has!

Thanks again

Mark