Using a stripe of mirrors (RAID0) you can get the benefits of multiple
spindle performance, easy expansion support (just add new mirrors to the
end of the raid0 stripe), and 100% data redundancy. If you can afford
to pay double for your storage (the cost of mirroring), this is IMO the
best solution.
Note that this solution is not quite as resilient against hardware
failure as raidz2 or raidz3. While the RAID1+0 solution can tolerate
multiple drive failures, if both both drives in a mirror fail, you lose
data.
If you're clever, you'll also try to make sure each side of the mirror
is on a different controller, and if you have enough controllers
available, you'll also try to balance the controllers across stripes.
One way to help with that is to leave a drive or two available as a hot
spare.
Btw, the above recommendation mirrors what Jeff Bonwick himself (the
creator of ZFS) has advised on his blog.
-- Garrett
On Thu, 2010-06-03 at 09:06 -0500, David Dyer-Bennet wrote:
> On Wed, June 2, 2010 17:54, Roman Naumenko wrote:
> > Recently I talked to a co-worker who manages NetApp storages. We discussed
> > size changes for pools in zfs and aggregates in NetApp.
> >
> > And some time before I had suggested to a my buddy zfs for his new home
> > storage server, but he turned it down since there is no expansion
> > available for a pool.
>
> I set up my home fileserver with ZFS (in 2006) BECAUSE zfs could expand
> the pool for me, and nothing else I had access to could do that (home
> fileserver, little budget).
>
> My server is currently running with one data pool, three vdevs. Each of
> the data vdev is a two-way mirror. I started with one, expanded to two,
> then expanded to three. Rather than expanding to four when this fills up,
> I'm going to attach a larger drive to the first mirror vdev, and then a
> second one, and then remove the two current drives, thus expanding the
> vdev without ever compromising the redundancy.
>
> My choice of mirrors rather than RAIDZ is based on the fact that I have
> only 8 hot-swap bays (I still think of this as LARGE for a home server;
> the competition, things like the Drobo, tends to have 4 or 5), that I
> don't need really large amounts of storage (after my latest upgrade I'm
> running with 1.2TB of available data space), and that I expected to need
> to expand storage over the life of the system. With mirror vdevs, I can
> expand them without compromising redundancy even temporarily, by attaching
> the new drives before I detach the old drives; I couldn't do that with
> RAIDZ. Also, the fact that disk is now so cheap means that 100%
> redundancy is affordable, I don't have to compromise on RAIDZ.
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