gvinum raid5 performance seems slow

[Eric Anderson]

On 10/27/06 18:03, Steve Peterson wrote:
> I recently set up a media server for home use and decided to try the 
> gvinum raid5 support to learn about it and see how it performs.  It 
> seems slower than I'd expect -- a little under 6MB/second, with about 
> 50 IOs/drive/second -- and I'm trying to understand why.  Any 
> assistance/pointers would be appreciated.
> 
> The disk system consists of 4 Seagate NL35 SATA ST3250623NS drives 
> connected to a Promise TX4300 (PDC40719) controller, organized as a 
> RAID5 volume via gvinum using this configuration:
> 
> drive drive01 device /dev/ad10
> drive drive02 device /dev/ad6
> drive drive03 device /dev/ad4
> drive drive04 device /dev/ad8
> 
> volume vol1
>    plex org raid5 256k
>      sd length 200001m drive drive01
>      sd length 200001m drive drive02
>      sd length 200001m drive drive03
>      sd length 200001m drive drive04
> 
> dd reports the following performance on a 1G file write to the RAID5 
> hosted volume:
> 
> $ time dd if=/dev/zero of=big.file bs=1m count=1000
> 1000+0 records in
> 1000+0 records out
> 1048576000 bytes transferred in 179.717742 secs (5834571 bytes/sec)
>        179.76 real         0.02 user        16.60 sys
> 
> By comparison, creating the same file on the system disk (an old ATA 
> ST380021A connected via a SIS 730 on the motherboard):
> 
> time dd if=/dev/zero of=big.file bs=1m count=1000
> 1000+0 records in
> 1000+0 records out
> 1048576000 bytes transferred in 28.264056 secs (37099275 bytes/sec)
>         28.32 real         0.01 user        19.13 sys
> 
> and vmstat reports about 280-300 IOs/second to that drive.
> 
> The CPU is pretty weak -- an Athlon 750.  Is that the source of my 
> problem?  If you look at the vmstat output below the machine is busy 
> but not pegged.


Try the dd to the raw gvinum device instead of through a filesystem, and 
also to the individual disks.  That will at least tell us where to look.


Eric



-- 
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Eric Anderson        Sr. Systems Administrator        Centaur Technology
Anything that works is better than anything that doesn't.
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