ZFS on Hardware RAID

[Steven Hartland]

On 21/01/2019 16:00, Gary Palmer wrote:
> On Mon, Jan 21, 2019 at 03:17:08PM +0100, Borja Marcos wrote:
>>
>>> 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.
> This is a pertinent point.  If I remember right, no LSI RAID controller
> supports TRIM/UNMAP on SSDs.  Spinning rust is OK in a RAID controller,
> but if you have SSDs attached to the LSI RAID controller and plan to use
> them in ZFS it is better to get a HBA instead.
LSI controllers, even RAID ones, when used in JBOD mode pass this 
information through correctly.

Even if its SATA disk, it should work after I added support to 
pass-through ATA command to CAM SCSI disk many years ago.

     Regards
     Steve