zfs discuss - May 2006 - zfs mirror/raidz: can they use different types of disks

Hi,

I just got an Ultra 20 with the default 80GB internal disk.  Right now, 
I''m using around 30GB for zfs.  I will be getting a new 250GB drive.

Question: If I create a 30GB slice on the 250GB drive, will that be okay 
to use as mirror (or raidz) of the current 30GB that I now have on the 
30GB drive?  I ask because if I remember correctly, some volume managers 
require(?) that mirrors should use drives with the same geometry.

Thanks.

James

ZFS doesn''t demand that the drives have the same capacity.  If you  
mirror a 30GB drive and a 40GB drive then ZFS will treat them as two  
30GB drives, so you''re effectively wasting 10GB of space.

Noel


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"Question all the answers"
On May 3, 2006, at 2:16 PM, James Foronda wrote:
> Hi,
>
> I just got an Ultra 20 with the default 80GB internal disk.  Right  
> now, I''m using around 30GB for zfs.  I will be getting a new 250GB
> drive.
>
> Question: If I create a 30GB slice on the 250GB drive, will that be  
> okay to use as mirror (or raidz) of the current 30GB that I now have  
> on the 30GB drive?  I ask because if I remember correctly, some volume  
> managers require(?) that mirrors should use drives with the same  
> geometry.
>
> Thanks.
>
> James
> _______________________________________________
> zfs-discuss mailing list
> zfs-discuss at opensolaris.org
> http://mail.opensolaris.org/mailman/listinfo/zfs-discuss

Should work just fine.
 
 
This message posted from opensolaris.org

> I just got an Ultra 20 with the default 80GB internal disk.  Right now, 
> I''m using around 30GB for zfs.  I will be getting a new 250GB
drive.
> 
> Question: If I create a 30GB slice on the 250GB drive, will that be okay 
> to use as mirror (or raidz) of the current 30GB that I now have on the 
> 30GB drive?  I ask because if I remember correctly, some volume managers 
> require(?) that mirrors should use drives with the same geometry.
Yes.  The size of a ZFS mirror is the size of its smallest member.
However, if you later replace the 30G slice with a shiny new 25G drive,
the mirror will automatically grow to make the full 250G available.

Jeff

On Thu, May 04, 2006 at 12:20:47AM -0700, Jeff Bonwick
wrote:
> > I just got an Ultra 20 with the default 80GB internal disk.  Right
now,
> > I''m using around 30GB for zfs.  I will be getting a new 250GB
drive.
> > 
> > Question: If I create a 30GB slice on the 250GB drive, will that be
okay
> > to use as mirror (or raidz) of the current 30GB that I now have on the
> > 30GB drive?  I ask because if I remember correctly, some volume
managers
> > require(?) that mirrors should use drives with the same geometry.
> 
> Yes.  The size of a ZFS mirror is the size of its smallest member.
> However, if you later replace the 30G slice with a shiny new 25G drive,
                                                               ^^^ 250G,
presumably?
> the mirror will automatically grow to make the full 250G available.
> 
> Jeff
> 
> _______________________________________________
> zfs-discuss mailing list
> zfs-discuss at opensolaris.org
> http://mail.opensolaris.org/mailman/listinfo/zfs-discuss
-- 
Jonathan Adams, Solaris Kernel Development

I was under the impresion that Raid-Z could also use disks of multiple sizes. 
Is that correct?  In other words, if I created a raidz pool with four disks of
80gb, 80gb, 160gb, 160gb, would I only get a useful pool of (4-1)*80gb = 240gb
or would I get (sum(80,80,160,160) - max(80,80,160,160)) = 320gb?
 
 
This message posted from opensolaris.org