[NTLUG:Discuss] SCSI performance question

[Leroy Tennison]

Robert Parkhurst wrote:
> I've used SCSI a lot, but mostly in the "lower-end" area (external CD/DVD
> SCSI drives, external SCSI hard drive or even a small SCSI external disk
> pack).  I'm curious though how SCSI would perform if you had a lot of large
> disk arrays attached off a single SCSI bus/adapter?
> 
> Specifically, say I had an LSI SCSI adapter (Ultra-320, PCI-e (x8)) that
> could have 32 SCSI devices attached to it.  And I attached 31x16TB external
> SCSI enclosures (like the JetStor SCSI unit or something) off that one
> adapter and then used Linux to make an LVM striped volume over all of them
> and formatted it with something like ReiserFS or XFS.  Would I see a
> (noticeable) performance hit on it?
> 
> And if so, what's a good "recommended" max for attaching storage like that
> to a single SCSI controller?
> 
> 
> 
> 
> Thanks in advance!
> 
> 
> Robert
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> 
This is almost impossible to answer because performance is affected by
too many variables: what are the capabilities of the SCSI controller
(caching and how much? is the firmware efficient? how many channels?
other performance characteristics), the SCSI drives (all the common hard
drive performance characteristics), how is it configured (RAID?  If so,
which level?) and what your application is (mainly read-only, lots of
writing, lots of deletions after writing, a database).  Further
complicating matters is the fact that it's not just individual issues
but combinations of them (matching the configuration and the hardware to
the application).