Date: Mon, 21 Jan 2019 15:40:18 +0000 From: Steven Hartland <killing@multiplay.co.uk> To: Borja Marcos <borjam@sarenet.es>, jdelisle <jdelisle@gmail.com> Cc: freebsd-fs <freebsd-fs@freebsd.org> Subject: Re: ZFS on Hardware RAID Message-ID: <335e44ec-7c76-8dbd-f587-46e6a9266efc@multiplay.co.uk> In-Reply-To: <92746659-4B3F-415C-BB6A-6C99837AFAF2@sarenet.es> References: <1180280695.63420.1547910313494.JavaMail.zimbra@gausus.net> <92646202.63422.1547910433715.JavaMail.zimbra@gausus.net> <CAOeNLurgn-ep1e=Lq9kgxXK%2By5xqq4ULnudKZAbye59Ys7q96Q@mail.gmail.com> <alpine.BSF.2.21.1901200834470.12592@mail0.time-domain.co.uk> <1691666278.63816.1547976245836.JavaMail.zimbra@gausus.net> <alpine.BSF.2.21.1901200930550.12592@mail0.time-domain.co.uk> <CAMdBLfQvF7mXriwAvu-h5BaXBNhb_8VPRRfDmeM0u1NGoyWY_g@mail.gmail.com> <92746659-4B3F-415C-BB6A-6C99837AFAF2@sarenet.es>
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On 21/01/2019 14:17, Borja Marcos wrote: > >> On 20 Jan 2019, at 16:33, jdelisle <jdelisle@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? Typically yes it does. > 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. > Indeed you can for most, but its not an easy or error free option, requires *force *flashing from IR to IT firmware, and if it goes wrong you can end up with a bricked controller. We've used LSI's in IR mode (RAID) but as individual disks JBOD with ZFS raid2z or mirroring on top for a long time and on lots of machines, not had any issues to report. So while I would never use hardware RAID from those controllers with ZFS, JBOD on them is an easy and reliable option in our experience. Regards Steve
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