zfs discuss - Aug 2007 - Simple RAID-Z question

Hey everybody,
I''m thinking of moving my file server (at home) from Linux to  
Solaris, mostly due to ZFS and DTrace.
One problem, though. I''ll start out with a ZFS pool on 2x200GB disks  
+ a 200GB slice/partition on a 250GB disk (with 50GB as system etc);  
that works, right? 400GB of storage and one disk can fail with no  
data loss, I suppose.
If so: what happens when I in the future add a fourth disk to the  
pool, probably a 500-750GB one? How much capacity will I get from the  
pool, and what happens if any given disk (including the new, bigger  
one) fails?

Thanks in advance,
Thomas

> One problem, though. I''ll start out with a ZFS pool on 2x200GB
disks
> + a 200GB slice/partition on a 250GB disk (with 50GB as system etc);
> that works, right? 400GB of storage and one disk can fail with no
> data loss, I suppose.
Assuming raidz, yes.
> If so: what happens when I in the future add a fourth disk to the
> pool, probably a 500-750GB one? How much capacity will I get from the
> pool, and what happens if any given disk (including the new, bigger
> one) fails?
A raidz/raidz2 will not expand further than the smallest disk in the set. So 
adding a 750 gb disk to an existing raidz/raidz2 pool with 200 gb drives, 
will not expand the set (though my understanding is that there is work 
planned or ongoing to add support for growing a raidz/raidz2 incrementally by 
adding drives).

Currently, in order to get more storage you have to either upgrade all drives 
in the set, or stripe the pool across multiple sets (so eg, you could add 
7x750 gb and have the pool striped over that and the 3x300 gb set).

-- 
/ Peter Schuller

PGP userID: 0xE9758B7D or ''Peter Schuller <peter.schuller at
infidyne.com>''
Key retrieval: Send an E-Mail to getpgpkey at scode.org
E-Mail: peter.schuller at infidyne.com Web: http://www.scode.org