[luau] improving sustainable write to disk rates

[Warren Togami]

On Wed, 2002-09-04 at 13:55, Charles Lockhart wrote:
> MonMotha wrote:
> 
> > What kind of SCSI?
> 
> The drives are ultra3, but while the array controller supports both 
> ultra2 and ultra3 drives, it makes everything run at ultra 2 speeds, or 
> something like that.  I read it somewhere in their spec but now I can't 
> find it.
> 

What kind of data writes will you be doing?  Mostly sequential, or
random?

I think modern SCSI drives (and even IDE drives) can sustain 40MB/sec
sequential with only a single disk.  What kind of speeds do you get with
a single disk on that SCSI controller?

At AMDMB we found one particular SCSI RAID controller (AMI MegaRAID) to
be extremely terrible.  In a RAID 1+0 configuration with four disks, we
were somehow getting only 5MB/sec.  Even after dozens of reboots and
hours on the phone with AMI tech support, we were unable to fix the
situation and moved to an Adaptec controller.

Alan Cox's diary mentioned something similar about a year ago.  He said
something about throwing out his AMI MegaRAID controller and using Linux
software RAID instead.  He got much better performance that way.