Date: Mon, 21 Jan 2019 20:05:27 +0000 From: Steven Hartland <killing@multiplay.co.uk> To: Gary Palmer <gpalmer@freebsd.org>, Borja Marcos <borjam@sarenet.es> Cc: freebsd-fs <freebsd-fs@freebsd.org> Subject: Re: ZFS on Hardware RAID Message-ID: <a460db2e-3e9e-127b-705d-c1e14d4c83af@multiplay.co.uk> In-Reply-To: <20190121160016.GC45377@in-addr.com> 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> <20190121160016.GC45377@in-addr.com>
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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@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
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