zfs discuss - Mar 2008 - Mixing RAIDZ and RAIDZ2 zvols in the same zpool

I have a customer who has implemented the following layout:  As you can 
see, he has mostly raidz zvols but has one raidz2 in the same zpool.  
What are the implications here?  Is this a bad thing to do? Please 
elaborate.

Thanks,

Scott Gaspard
Scott.J.Gaspard at Sun.COM
>       NAME        STATE     READ WRITE CKSUM
>
>         chipool1    ONLINE       0     0     0
>
>           raidz2    ONLINE       0     0     0
>
>             c0t0d0  ONLINE       0     0     0
>
>             c1t0d0  ONLINE       0     0     0
>
>             c4t0d0  ONLINE       0     0     0
>
>             c6t0d0  ONLINE       0     0     0
>
>             c7t0d0  ONLINE       0     0     0
>
>             c1t4d0  ONLINE       0     0     0
>
>             c6t4d0  ONLINE       0     0     0
>
>           raidz1    ONLINE       0     0     0
>
>             c0t1d0  ONLINE       0     0     0
>
>             c1t1d0  ONLINE       0     0     0
>
>             c4t1d0  ONLINE       0     0     0
>
>             c5t1d0  ONLINE       0     0     0
>
>             c6t1d0  ONLINE       0     0     0
>
>             c7t1d0  ONLINE       0     0     0
>
>           raidz1    ONLINE       0     0     0
>
>             c0t2d0  ONLINE       0     0     0
>
>             c1t2d0  ONLINE       0     0     0
>
>             c4t2d0  ONLINE       0     0     0
>
>             c5t2d0  ONLINE       0     0     0
>
>             c6t2d0  ONLINE       0     0     0
>
>             c7t2d0  ONLINE       0     0     0
>
>           raidz1    ONLINE       0     0     0
>
>             c0t3d0  ONLINE       0     0     0
>
>             c1t3d0  ONLINE       0     0     0
>
>             c4t3d0  ONLINE       0     0     0
>
>             c5t3d0  ONLINE       0     0     0
>
>             c6t3d0  ONLINE       0     0     0
>
>             c7t3d0  ONLINE       0     0     0
>
>           raidz1    ONLINE       0     0     0
>
>             c0t5d0  ONLINE       0     0     0
>
>             c1t5d0  ONLINE       0     0     0
>
>             c4t5d0  ONLINE       0     0     0
>
>             c5t5d0  ONLINE       0     0     0
>
>             c6t5d0  ONLINE       0     0     0
>
>             c7t5d0  ONLINE       0     0     0
>
>           raidz1    ONLINE       0     0     0
>
>             c0t6d0  ONLINE       0     0     0
>
>             c1t6d0  ONLINE       0     0     0
>
>             c4t6d0  ONLINE       0     0     0
>
>             c5t6d0  ONLINE       0     0     0
>
>             c6t6d0  ONLINE       0     0     0
>
>             c7t6d0  ONLINE       0     0     0
>
>           raidz1    ONLINE       0     0     0
>
>             c0t7d0  ONLINE       0     0     0
>
>             c1t7d0  ONLINE       0     0     0
>
>             c4t7d0  ONLINE       0     0     0
>
>             c5t7d0  ONLINE       0     0     0
>
>             c6t7d0  ONLINE       0     0     0
>
>             c7t7d0  ONLINE       0     0     0
>
>         spares
>
>           c4t4d0    AVAIL
>
>           c7t4d0    AVAIL

Hello Scott,

Wednesday, March 12, 2008, 4:41:21 PM, you wrote:

SG> I have a customer who has implemented the following layout:  As you can
SG> see, he has mostly raidz zvols but has one raidz2 in the same zpool.  
SG> What are the implications here?  Is this a bad thing to do? Please 
SG> elaborate.

Well, it will work. Just slightly strange configuration but shouldn''t
do any negative impact. Theoretically performance could be slightly
worse, but probably nothing to worry much about.

All groups provide the same space so there shouldn''t be any problem
with balancing data.

IMHO - it''s fine - little bit strange but fine.


-- 
Best regards,
 Robert Milkowski                           mailto:milek at task.gda.pl
                                       http://milek.blogspot.com

On Wed, Mar 12, 2008 at 11:41:21AM -0500, Scott Gaspard
wrote:
> I have a customer who has implemented the following layout:  As you can 
> see, he has mostly raidz zvols but has one raidz2 in the same zpool.  
> What are the implications here?  Is this a bad thing to do? Please 
> elaborate.
It''s not *bad*, but as far as I''m concerned, it''s
wasted space.

You have to deal with the pool as a whole as having single-disk
redundancy for failure modes.  So the fact that one section of it has
two-disk redundancy doesn''t give you anything in failure planning.

And you can''t assign filesystems or particular data to that vdev, so
the
added redundancy can''t be concentrated anywhere.

-- 
Darren Dunham                                           ddunham at taos.com
Senior Technical Consultant         TAOS            http://www.taos.com/
Got some Dr Pepper?                           San Francisco, CA bay area
         < This line left intentionally blank to confuse you. >

On Wed, Mar 12, 2008 at 09:59:53PM +0000, A Darren Dunham
wrote:
> It''s not *bad*, but as far as I''m concerned,
it''s wasted space.
> 
> You have to deal with the pool as a whole as having single-disk
> redundancy for failure modes.  So the fact that one section of it has
> two-disk redundancy doesn''t give you anything in failure planning.
> 
> And you can''t assign filesystems or particular data to that vdev,
so the
> added redundancy can''t be concentrated anywhere.
Well, one can imagine a situation where two different type of disks have
different failure probabilities such that the same reliability could be
garnered with one using single-parity RAID as with the other using double-
parity RAID. That said, it would be a fairly uncommon scenario.

Adam

-- 
Adam Leventhal, Fishworks                        http://blogs.sun.com/ahl