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SubjectRe: Linux MD RAID 5 Benchmarks Across (3 to 10) 300 Gigabyte Veliciraptors
Justin Piszcz wrote:
>
>
> On Wed, 11 Jun 2008, Justin Piszcz wrote:
>
>>
>>
>> On Wed, 11 Jun 2008, Bill Davidsen wrote:
>>
>>> Justin Piszcz wrote:
>>>> First, the original benchmarks with 6-SATA drives with fixed
>>>> formatting, using
>>>> right justification and the same decimal point precision throughout:
>>>> http://home.comcast.net/~jpiszcz/20080607/raid-benchmarks-decimal-fix-and-right-justified/disks.html
>>>> Now for for veliciraptors! Ever wonder what kind of speed is
>>>> possible with
>>>> 3 disk, 4,5,6,7,8,9,10-disk RAID5s? I ran a loop to find out, each
>>>> run is
>>>> executed three times and the average is taken of all three runs per
>>>> each RAID5 disk set.
>>>>
>>>> In short? The 965 no longer does justice with faster drives, a new
>>>> chipset
>>>> and motherboard are needed. After reading or writing to 4-5
>>>> veliciraptors
>>>> it saturates the bus/965 chipset.
>>>
>>> This is very interesting, but a 16GB chunk size bears no
>>> relationship to anything I would run in the real world, and I
>>> suspect most people are in the same category.
>>
>> I based my bonnie++ test on:
>> http://everything2.org/?node_id=1479435
>>
>> So I could compare to his results.
>>
>> I use a 1024k (1MiB) with 16384 stripe, this offered the best overall
>> read/write/rewrite performance AFAIK.
>
> 1024k chunk size (raid5 chunk size)
> echo 16384 > stripe_cache_size

Please don't explain any more, I'm confused enough already. I can't make
those numbers match 16G no matter how I add them, either the contents of
the column labeled "size:chunk size" isn't the size of the chunk, or you
have a multiplier floating around that I don't see. And you eliminated
the degraded performance, since your stripe_cache_size is less than
(raid5 chunk size)*(#disks), I would expect the reads in degraded mode
to be dog slow because the don't fit in cache, even if 1024k is what I
call chunk size and certainly not if chunk size is 16G.

--
Bill Davidsen <davidsen@tmr.com>
"Woe unto the statesman who makes war without a reason that will still
be valid when the war is over..." Otto von Bismark




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