ZFS on Hardware RAID

[jdelisle]

On Sun, Jan 20, 2019 at 9:04 AM andy thomas <andy at time-domain.co.uk> wrote:

> I don't h/w RAID controllers do any parity checking, etc for RAID 0
> virtual disks containing only one disk?
>

I can say for certain that with Dell PERC 6/e RAID (SAS 8087ELP based)
cards, when the virtual devices are entire disks each in a RAID0
configuration, the way the adapter writes data to them is effectively the
same as JBOD.  You can take a RAID0 drive from a PERC 6/e controller and
use in with an HBA/ "IT Mode" JBOD controller without issue.  I personally
migrated 14x 1TB drives off PERC 6/e (all RAID0's) to a SAS 6gbps HBA, and
my ZFS VDEV's and pools were totally fine.  You can move back and forth no
problem.  I can't say this is the case for ALL RAID controllers, I've only
done this with an old PERC 6/e.



> I know ZFS on h/w raid can't possibly be optimal and use of JBOD,
> pass-thru or plain HBA is to be preferred at all times but older RAID
> controllers don't support non-RAID operation - after all, h/w RAID
> controller design is primarily intended for the Windows Server market
> where Windows didn't support any kind of software RAID scheme at that time
> (it might do know, I don't know).
>

That's why I did as I describe above.  I didn't have the money to buy an
HBA until a year or two later, and I had good backups, so I used the PERC
6/e.