ZFS on Hardware RAID

[Borja Marcos]

> On 20 Jan 2019, at 16:33, jdelisle <jdelisle at gmail.com> wrote:
> 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.

However a single disk RAID0 volume (what manufacturers call a JBOD) is not the same 
as a disk. With the “virtual JBOD” you lose direct CAM access, which means that some
advanced options won’t be supported.

For example, if you are using SSDs ZFS knows when to issue a TRIM (or, in general,
BIO_DELETE) command. Does the “virtual JBOD” offer that option? 

The same could be said of other functionalities available when you talk directly
to the disks.


> 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.

Depending on the LSI model used in that card you can make it behave like an HBA. 





Borja.