Lee Marzke on 2 Aug 2009 17:05:29 -0700

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Re: [PLUG] ZFS is not a backup

Sean Collins wrote:
> Had a user with an OS X box that was using ZFS to mirror a dataset.  
> User had a hardware failure (disks were in the same enclosure) that  
> corrupted the ZFS metadata. He had not archived his data, so once  
> again we are left to remind others that RAID and other replication  
> strategies are to prevent downtime. Nothing more!
> Not to mention, ZFS support on OS X has become very unofficial over  
> the past few months. I use ZFS on my OS X laptop but I made an archive  
> of all my data just in case something catastrophic happened.
> Thank You,
> Sean Collins

I've been playing with ZFS lately in a VM, yes  Lots of misconceptions
about ZFS.

By itself ZFS includes volume management and a file system, but ZFS
alone is not RAID.
The  RAID-Z component is what provides the redundancy,  but as Jeff
Darcy  blog points out here http://pl.atyp.us/wordpress/?p=1009   there
is controversy if RAID-Z is really RAID at all.

Conceptually it's easy to rebuild a mirror, or RAID 5 array,  but the
argument is that rebuilding a ZFS disk requires traversing the entire
filesystem tree,  so the rebuild could be more prone fail for other
unknown errors.

Still,  the write performance is much better than RAID-5 ,  the RAID-5
write hole is plugged, snapshots are inexpensive and incur no
performance penalty,  and the command-line management
tools are very easy to work with.

And yes, if your snapshotting locally,  then use ZFS snapshot replication
to get the data onto another separate device.

fn:Lee Marzke
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