Re: Slow Soft-RAID 5 performance

[Justin Piszcz]

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.

Justin.

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