Re: Slow Soft-RAID 5 performance

[Justin Piszcz <jpiszcz@lucidpixels.com>]

On Thu, 19 Jul 2007, Lars Schimmer wrote:

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> Justin Piszcz wrote:
>>
>>
>> On Wed, 18 Jul 2007, Rui Santos wrote:
>>
>>> Hi,
>>>
>>> I'm getting a strange slow performance behavior on a recently installed
>>> Server. Here are the details:
>>>
>>> Server: Asus AS-TS500-E4A
>>> Board: Asus DSBV-D (
>>> http://uk.asus.com/products.aspx?l1=9&l2=39&l3=299&l4=0&model=1210&modelmenu=2
>>>
>>> )
>>> Hard Drives: 3x Seagate ST3400620AS (
>>> http://www.seagate.com/ww/v/index.jsp?vgnextoid=8eff99f4fa74c010VgnVCM100000dd04090aRCRD&locale=en-US
>>>
>>> )
>>> I'm using the AHCI driver, although with ata_piix, the behavior is the
>>> same. Here's some info about the AHCI controler:
>>>
>>
>> With three disks, if everything was perfect yeah 120MB/s writes.  When I
>> had started out with 4 raptors I was getting 164MB/s read and write.  By
>> default with no optimizations you will not get good speed.
>>
>> With no optimizations with 10 raptors I get 180-200MB/s, with
>> optimizations, 464MB/s write and 622MB/s read.
>>
>> 1. Use XFS if you wan't speed.
>> 2. Use 128k, 256k or 1MiB chunk size.
>> 3. Use 8192k, 16384k stripe_cache_size.
>> 4. Use 65536 readahead size.
>>
>> These are only some of the optimizations I use.
>
> One question in between, which option of these I can set after RAID5 is
> filled with data?
> E.G. I setup a 9 disk SOFT-RAID5 with XFS and 3125669888 blocks level 5,
> 128k chunk, algorithm 2 [9/9] [UUUUUUUUU].
> Speed is not really fast, I assume it could be faster.

You can experiment with the stripe_cache_size and readahead size to
start with.

Justin.