zfs discuss - Aug 2006 - Best Practices for StorEdge 3510 Array and ZFS

I have a StorEdge 3510 FC array which is currently configured in the following
way:

* logical-drives 

LD    LD-ID        Size  Assigned  Type   Disks Spare  Failed Status     
------------------------------------------------------------------------
ld0   255ECBD0   2.45TB  Primary   RAID5  10    2      0      Good  
                         Write-Policy Default          StripeSize 128KB


What are the best practices of using ZFS on this array so that I can benefit
from both ZFS and HW RAID?

Thanks in advance,
-- prasad
 
 
This message posted from opensolaris.org

prasad wrote:
> I have a StorEdge 3510 FC array which is currently configured in the
following way:
>
> * logical-drives 
>
> LD    LD-ID        Size  Assigned  Type   Disks Spare  Failed Status     
> ------------------------------------------------------------------------
> ld0   255ECBD0   2.45TB  Primary   RAID5  10    2      0      Good  
>                          Write-Policy Default          StripeSize 128KB
>
>
> What are the best practices of using ZFS on this array so that I can
benefit from both ZFS and HW RAID?
Are any other hosts using the array? Do you plan on carving LUNs out of 
the RAID5 LD and assigning them to other hosts?

Torrey McMahon <Torrey.McMahon at Sun.COM> 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.

-- prasad
 
 
This message posted from opensolaris.org

On Aug 2, 2006, at 17:03, prasad wrote:
> Torrey McMahon <Torrey.McMahon at Sun.COM> 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