On Aug 2, 2006, at 17:03, prasad wrote:
Torrey McMahon <[EMAIL PROTECTED]> wrote:
Are any other hosts using the array? Do you plan on carving LUNs
out of
the RAID5 LD and assigning them to other hosts?
There are no other hosts using the array. We need all the available
space (2.45TB) on just one host. One option was to create 2 LUN's
and use raidz.
raidz on RAID5 isn't very efficient and you'll want at least 3 lun's
to do it .. you're calculating double parity and tying up too much of
your drive bandwidth.
if you're going to some variation of RAID5 the best throughput you'll
see is to *either* pick the HW RAID characteristics *or* ZFS raidz ..
but not both .. if you want a *lot* of redundancy you could create a
bunch of RAID10 volumes and then do a raidz on the zpool - but you're
really going to lose a lot of capacity that way.
What you really want to do is make efficient use of the array cache
*and* the copy on write zfs "cache" so you're doing mostly memory to
memory transfers. so that leaves us with 2 options (each with slight
variations)
option 1 - raidz:
I would use all the disks in the 3510 to make either 4 x 3 disk or 6
x 2 disk R0 volumes and balance them across the controllers (assuming
you have 2) .. then create your raidz zpool out of all the disks ..
the disadvantage (or advantage depending on how you look at it) here
is that you're not using the parity engine in the 3510 and you can't
really hot spare from the array.. the advantage though is the
software based error correction you'll be able to do.
option 2 - RAID5
either use the volume you already have or make 2 R5 volumes if you
have 2 controllers to balance the LUNs .. it won't matter if they're
the same size or not, and you should only really need 1 global hot
spare .. then create a standard zpool with these .. the disadvantage
is that you won't get the lovely raidz features .. but the possible
advantage is that you've offloaded the parity calculation and
workload from the host
Keep in mind that zfs was originally designed with JBOD in mind ..
there's still ongoing discussions on how hw RAID fits into the
picture with the new and lovely sw raidz and whether or not socks
will be worn when testing one vs the other ..
---
.je
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