LSI SATA Raid - slow

[Hans du Plooy <hansdp-lists@sagacit.com>]

Hi all,

I'm building a backup server for a client - straight forward as far as 
software goes - samba share for the daily backups to go into.   Minimal 
install plus sarge.

Hardware is a 2ghz Celeron (P4 type), 256MB ram, and four Seagate 160GB 
SATA discs in a RAID-5 on this controller:

000:00:07.0 RAID bus controller: LSI Logic / Symbios Logic MegaRAID (rev 
01)
      Subsystem: LSI Logic / Symbios Logic MegaRAID SATA 150-6 RAID 
Controller
      Flags: bus master, 66Mhz, slow devsel, latency 32, IRQ 11
      Memory at ef000000 (32-bit, prefetchable) [size=64K]
      Capabilities: [80] Power Management version 2

The card uses the LSI raid chip for raid, and three Silicon Image 3112a 
chips for SATA itself.  I have a Sil_3112a card and I know it works as 
it should.

I copied the data that was on the original RAID set (3 discs) off to a 
200gb Seagate PATA disc, and mc reported on the large files 27mb/s 
sustained write.

Now, copying stuff back to the RAID set, mc reports a mere 6-7mb/s.

The only thing that struck me as weird is that the controller didn't 
take much time to create the raid - less than a minute.  Last time I 
made a raid (2 10krpm SCSI 74gb discs on an Adaptec card) that took a 
couple of hours.   It seems like this controller does it in the 
background, because I can constantly hear the discs going krr krr krr.  
But it's been doing that since friday, and I would have thought it 
should be done by now.

Any ideas why I'm getting this?  7mb/s write is not going to be enough 
to copy all the data before the next backup starts.

Thanks
Hans