Wee Yeh Tan writes:
> On 9/5/06, Torrey McMahon <Torrey.McMahon@xxxxxxx> wrote:
> > This is simply not true. ZFS would protect against the same type of
> > errors seen on an individual drive as it would on a pool made of HW raid
> > LUN(s). It might be overkill to layer ZFS on top of a LUN that is
> > already protected in some way by the devices internal RAID code but it
> > does not "make your data susceptible to HW errors caused by the storage
> > subsystem's RAID algorithm, and slow down the I/O".
> & Roch's recommendation to leave at least 1 layer of redundancy to ZFS
> allows the extension of ZFS's own redundancy features for some truely
> remarkable data reliability.
> Perhaps, the question should be how one could mix them to get the best
> of both worlds instead of going to either extreme.
> > True, ZFS can't manage past the LUN into the array. Guess what? ZFS
> > can't get past the disk drive firmware either....and thats a good thing
> > for all parties involved.
> Just me,
> Wire ...
> zfs-discuss mailing list
Thinking some more about this. If your requirements does
mandate some form of mirroring, then it truly seems that ZFS
should take that in charge if only because of the
self-healing characteristics. So I feel the storage array's
job is to export low latency Luns to ZFS.
I'd be happy to live with those simple Luns but I guess some
storage will just refuse to export non-protected luns. Now
we can definitively take advantage of the Array's capability
of exporting highly resilient Luns; RAID-5 seems to fit the
bill rather well here. Even an 9+1 luns will be quite
resilient and have a low block overhead.
So we benefit from the arrays resiliency as well as it's low
latency characteristics. And we mirror data at the ZFS level
which means great performance and great data integrity and
Note that ZFS write characteristics (all sequential) means
that we will commonly be filling full stripes on the luns
thus avoiding the partial stripe performance pitfall.
If you must shy away from any form of mirroring, then it's
either stripe your raid-5 luns (performance edge for those
who live dangerously) or raid-z around those raid-5 luns
(lower cost, survives lun failures).
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