Request for opinions - gvinum or ccd?

[Freddie Cash]

On Sat, Jun 6, 2009 at 12:54 PM, Ivan Voras<ivoras at freebsd.org> wrote:
> Sorry to come into the discussion late, but I just want to confirm
> something.
>
> The configuration below is a stripe of four components, each of which is
> RAIDZ2, right?
>
> If, as was discussed later in the thread, RAIDZ(2) is more similar to
> RAID3 than RAID5 for random performance, the given configuration can be
> (very roughly, in the non-sequential access case) expected to deliver
> performance of four drives in a RAID0 array?

According to all the Sun documentation, the I/O throughput of a raidz
configuration is equal to that of a single drive.

Hence their recommendation to not use more than 8 or 9 drives in a
single raidz vdev, and to use multiple raidz vdevs.  As you add vdevs,
the throughput increases.

We made the mistake early on of creating a 24-drive raidz2 vdev.
Performance was not very good.  And when we had to replace a drive, it
spent over a week trying to resilver.  But the resilver operation has
to touch every single drive in the raidz vdev.  :(

We remade the pool using 3x 8-drive raidz2 vdevs, and performance has
been great (400 MBytes/s write, almost 3 GBytes/s sequential read, 800
MBytes/s random read).

-- 
Freddie Cash
fjwcash at gmail.com