On May 1, 2009, at 2:09 AM, Wilkinson, Alex wrote:
0n Thu, Apr 30, 2009 at 11:11:55AM -0500, Bob Friesenhahn wrote:
On Thu, 30 Apr 2009, Wilkinson, Alex wrote:
I currently have a single 17TB MetaLUN that i am about to present
to an
OpenSolaris initiator and it will obviously be ZFS. However, I am
constantly
reading that presenting a JBOD and using ZFS to manage the RAID is
best
practice ? Im not really sure why ? And isn't that a waste of a
high performing
RAID array (EMC) ?
The JBOD "advantage" is that then ZFS can schedule I/O for the disks
and there is less chance of an unrecoverable pool since ZFS is
assured
to lay out redundant data on redundant hardware and ZFS uses more
robust error detection than the firmware on any array. When using
mirrors there is considerable advantage since writes and reads can be
concurrent.
That said, your EMC hardware likely offers much nicer interfaces for
indicating and replacing bad disk drives. With the ZFS JBOD approach
you have to back-track from what ZFS tells you (a Solaris device ID)
and figure out which physical drive is not behaving correctly. EMC
tech support may not be very helpful if ZFS says there is something
wrong but the raid array says there is not. Sometimes there is value
with taking advantage of what you paid for.
So, shall I forget ZFS and use UFS ?
Not at all. Just export lots of LUNs from your EMC to get the IO
scheduling win, not one giant one, and configure the zpool as a stripe.
/dale
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