number of disks to stripe on a channel

[Jim Smith]

Whats the optimum number of disks to stripe an lvol over on a single SCSI channel ?

[Stefan Farrelly]

Ive experimented with this before and I recall its about 2-3 only. Any more and it seems to flood the bus too much and actually slows down. Of course the best is to stripe over lots of disks over many channels but thats another story.

[Ken Scharpell · Accepted solution]

I think its around 4. Test it, create an lvol with 2, the do some dd's of the raw lvol and time them, then try 3,4,5 etc. and you will soon find the fastest. It depends on the speed of your disks and SCSI controller.

[Dave Wherry]

For SCSI the long standing recomendation has been to only have about 4, maybe 5 devices on a channel. So it seems you would not want to stripe over more than 5. With the newer, faster disks you might be able to get away with more disks on a channel. I'd stay a little more conservative though.

I've not actually experimented with it, however I was once told that stripping on just 2 disks provides little if any benefit. It almost thrashes the disks.
From that I would say to stripe over 3 to 4 or 3 to 5.
As Stefan said where you really gain on performance is when you are able to stripe over multiple controllers and disks. If you only have the single controller it somewhat limits you.