just beeing curious:

does your SATA controller and disks support NCQ/TCQ and ist either of them 
enabled?
Is write cache on Disks enabled?

I am only extrapolating from SCSI experiences - command queuing and disk write 
cache can slow-down the raid (if both inactive)

Juraj

> -----Ursprüngliche Nachricht-----
> Von: ADSM: Dist Stor Manager [mailto:ADSM-L AT VM.MARIST DOT EDU] Im 
> Auftrag von John Monahan
> Gesendet: Dienstag, 20. Juni 2006 21:35
> An: ADSM-L AT VM.MARIST DOT EDU
> Betreff: Re: TSM diskpool on SATA
> 
> > Did you do any FILE devclass work?  It sounds as though 
> your miserable 
> > performance was head thrashing, which we'd get in multiple LV DISK 
> > devclasses, and also in FILE devclasses.  Darn. :)
> 
> No I was using a DISK devclass, but I'm almost positive it 
> wouldn't have made any difference with FILE devclasses.  Some 
> of the LUNs were faster than others (first ones in the RAID 
> group created) and as soon as I was writing to more than one 
> at a time my performance would tank even further, which 
> shouldn't be any different had I used FILE devclasses.  I 
> would have tried file devclasses with more time for 
> performance reasons, but I had spent too much time on it 
> already and the 150 MB/sec writes for my diskpool was 
> adequate for my needs and outpaced the capabilities of my 
> single Gigabit network connection to the TSM server, so I moved on.
> 
> Hundreds of LVs with FILE devclasses on fibre disks would 
> probably do exactly what you are looking for and provide 
> excellent performance.  SATA just isn't good enough at 
> multiple, simultaneous I/Os to the same set of disks yet.
>