ZFS on Hardware RAID

[Ira Cooper]

Well put.

In addition, by using a raid controller, you are likely depriving the OS
and ZFS the ability to use the drive's writeback caches, and queue depth
management.

Cheers,

-Ira

On Sat, Jan 19, 2019 at 3:09 PM Rich <rincebrain at gmail.com> wrote:

> The two caveats I'd offer are:
> - RAID controllers add an opaque complexity layer if you have problems
> - e.g. if you're using single-disk RAID0s to make a RAID controller
> pretend to be an HBA, if the disk starts misbehaving, you have an
> additional layer of behavior (how the RAID controller interprets
> drives misbehaving and shows that to the OS) to figure out whether the
> drive is bad, the connection is loose, the controller is bad, ...
> - abstracting the redundancy away from ZFS means that ZFS can't
> recover if it knows there's a problem but the underlying RAID
> controller doesn't - that is, say you made a RAID-6, and ZFS sees some
> block fail checksum. There's not a way to say "hey that block was
> wrong, try that read again with different disks" to the controller, so
> you're just sad at data loss on your nominally "redundant" array.
>
> - Rich
>
> On Sat, Jan 19, 2019 at 11:44 AM Maciej Jan Broniarz <gausus at gausus.net>
> wrote:
> >
> > Hi,
> >
> > I want to use ZFS on a hardware-raid array. I have no option of making
> it JBOD. I know it is best to use ZFS on JBOD, but
> > that possible in that particular case. My question is - how bad of an
> idea is it. I have read very different opinions on that subject, but none
> of them seems conclusive.
> >
> > Any comments and especially case studies are most welcome.
> > All best,
> > mjb
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