ZFS RaidZ2 with 24 drives?
Matt Simerson
matt at corp.spry.com
Wed Dec 16 23:19:42 UTC 2009
On Dec 16, 2009, at 1:20 PM, Thomas Burgess wrote:
> On Wed, Dec 16, 2009 at 3:43 PM, Matt Simerson <matt at corp.spry.com>
> wrote:
>
> On Dec 15, 2009, at 3:52 PM, Solon Lutz wrote:
>
> Why do you use JBOD? You can configure a passthrough for all drives,
> explicitly degrading the Areca to a dumb sata controller...
>
> Why would I bother? Both ways present each disk to FreeBSD. Based
> on my understanding (and an answer received from Areca support), the
> only reason I'd bother manually configuring some disks for
> passthrough is if I wanted to use some disks in a RAID array and
> others as raw disks. Configuring JBOD mode configures ALL the disks
> on the controller as passthrough devices.
>
> I think the main reason is that ZFS is better when it has raw drives.
I've heard that numerous times. Perhaps it is true in some cases. Such
as when using a RAID controller from 1999. Or a $30 RAID adapter.
I've built several ZFS systems using on-board SATA/SAS controllers, a
couple of 24-disk systems with the Marvell SATA controllers used in
the Sun x4500, and three 24-disk systems using the Areca 1231ML. Using
the Areca as a hardware RAID controller with RAID volumes has proven
to perform better and be much more reliable than when using raw disks.
> Some of the features of ZFS don't work as well without having access
> to the drives in this way, and other features don't work at all.
The last time I compared the performance of ZFS using dumb Marvell
SATA controllers versus the Areca with RAID, them features you speak
of weren't worth the bits used to say them. On the two systems I
described in this thread, the one using RAID significantly outperforms
the one configured as JBOD. And in the case of the Areca, JBOD =
passthrough = raw disks.
> In general, it's always best to let ZFS handle the raid stuff and
> not use the hardware raid settings.
Because you said so?
I'd like to see some evidence to back that statement up. The only time
I've seen better ZFS performance numbers than what I'm getting with
FreeBSD 8 ZFS + Areca RAID6 is when I tested OpenSolaris with them
Marvell SATA controllers. But that was in August of 2008, and ZFS on
FreeBSD performs much better now. Some updated benchmarks would be
welcome.
Matt
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