ZFS RaidZ2 with 24 drives?

[Danny Carroll]

On 17/12/2009 6:43 AM, Matt Simerson wrote:
> 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.
>

It's my experience that the statement above is simply not true.  I
confirmed this with throughput tests as well as talking to Areca (as I
understand you also did).
JBOD = Give the OS the drive.
PassThrough = Give the OS the drive but run it through the cache first.

I use passthrough specifically for this reason.   If I lose power, then
the cache should fix up the writes at restart.

You do not have this protection when ZFS has access to the raw devices. 
Even worse if the devices write cache is turned on.

-D