gmirror on a slice uncertainty

[Pawel Jakub Dawidek]

On Fri, Jun 29, 2007 at 10:52:36PM -0700, Arne Wörner wrote:
> --- Pawel Jakub Dawidek <pjd at FreeBSD.org> wrote:
> > On Fri, Jun 29, 2007 at 07:46:33AM -0700, Arne Wörner wrote:
> > [...]
> > > I wouldnt use a bsdlabel on the gmirror device
> > 
> > Why? It's perfectly safe and useful.
> >
> Because he wants to use the whole device for his "home" file system...
> So he just introduces a 16 sectors offset...

Both methods (mirroring entire disks and mirroring only
slices/partitions) have pros and cons.
Mirroring entire disks:
- after a crash/power failure entire disk has to be synchronized, which may
  take a long time,
+ when one replaces disk, he doesn't have to configure slices/partitions
  on new disk, because everything will be synchronized,
+ after a crash/power failure there will be only one synchronization process
  running for the disks.
Mirroring slices/partitions:
+ after crash/power failure only those partitions that were actively used
  will be synchronized (gmirror marks devices as clean where there are
  no writes in few seconds)
- when one replaces disk, slices and partitions need to be configured by
  hand, and all partitions inserted to existing mirrors,
- after a crash/power failure gmirror will synchronize all partitions at
  once which puts very heavy load on disks - this should be corrected in
  the future and currently may be worked around.
+ allows for fancy configurations - I've machine with five disks, that
  have two 'a' partitions mirrored for root, three 'a' partition in
  graid3 for /usr/ and five 'd' partitions in ZFS/RAIDZ for /usr/home/.

I use both methods depending on my needs.

-- 
Pawel Jakub Dawidek                       http://www.wheel.pl
pjd at FreeBSD.org                           http://www.FreeBSD.org
FreeBSD committer                         Am I Evil? Yes, I Am!
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