On Tue, Sep 16, 2008 at 10:03 PM, Ben Rockwood <[EMAIL PROTECTED]> wrote: > gm_sjo wrote: >> 2008/9/15 gm_sjo: >> >>> 2008/9/15 Ben Rockwood: >>> >>>> On Thumpers I've created single pools of 44 disks, in 11 disk RAIDZ2's. >>>> I've come to regret this. I recommend keeping pools reasonably sized >>>> and to keep stripes thinner than this. >>>> >>> Could you clarify why you came to regret it? I was intending to create >>> a single pool for 8 1TB disks. >>> >> >> Sorry, just bouncing the back for Ben incase he missed it. >> > > No, I didn't miss it, just was hoping I could get some benchmarking in > to justify my points. > > > You want to keep stripes wide to reduce wasted disk space.... but you > also want to keep them narrow to reduce the elements involved in parity > calculation. In light home use I don't see a problem with an 8 disk > RAIDZ/RAIDZ2. If your serving in a multi-user environment your primary > concern is to reduce the movement of the disk heads, and thus narrower > stripes become adventagious.
I'm not sure that the width of the stripe is directly a problem. But what is true is that the random read performance of raidz1/2 is basically that of a single drive, so having more vdevs is better. Given a fixed number of drives, more vdevs implies narrower stripes, but that's a side-effect rather than a cause. For what it's worth, we put all the disks on our thumpers into a single pool - mostly it's 5x 8+1 raidz1 vdevs with a hot spare and 2 drives for the OS and would happily go much bigger. -- -Peter Tribble http://www.petertribble.co.uk/ - http://ptribble.blogspot.com/ _______________________________________________ zfs-discuss mailing list zfs-discuss@opensolaris.org http://mail.opensolaris.org/mailman/listinfo/zfs-discuss
