Terrible ix performance

[Peter Wemm]

On Wed, Jul 3, 2013 at 8:41 PM, Lawrence Stewart <lstewart at freebsd.org> wrote:

> - I recall some advice that zpool's should not have more than about 8 or
> 10 disks in them, and you should instead create multiple zpools if you
> have more disks. Perhaps investigate the source of that rumour and if
> it's true, try create 2 x 8 disk zpools in Box A and 3 x 8 disk zpools
> in box B and see if that changes things at all.

http://nex7.blogspot.com/2013/03/readme1st.html

Item #1:

"1. Virtual Devices Determine IOPS
IOPS (I/O per second) are mostly a factor of the number of virtual
devices (vdevs) in a zpool. They are not a factor of the raw number of
disks in the zpool. This is probably the single most important thing
to realize and understand, and is commonly not.

ZFS stripes writes across vdevs (not individual disks). A vdev is
typically IOPS bound to the speed of the slowest disk within it. So if
you have one vdev of 100 disks, your zpool's raw IOPS potential is
effectively only a single disk, not 100.
" -- end quote

I made this mistake myself a number of times before I found out.

-- 
Peter Wemm - peter at wemm.org; peter at FreeBSD.org; peter at yahoo-inc.com; KI6FJV
UTF-8: So you can \342\200\231 .. for when a ' just won't do