Re: Slow Soft-RAID 5 performance

[Rui Santos <rsantos@grupopie.com>]

Lars Schimmer wrote:
> 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 chage values from 3) and 4) on the fly by echoing values to:
3)
/sys/block/md?/md/stripe_cache_size

4)
/sys/block/<harddrive>/queue/read_ahead_kb

About option 2) I don't how to reconfigure that. I used the following:
tar
make new raid with correct option
untar

>
>
> > Justin.
Rui
>
>
> MfG,
> Lars Schimmer