Date: Mon, 21 Jan 2019 15:17:08 +0100 From: Borja Marcos <borjam@sarenet.es> To: jdelisle <jdelisle@gmail.com> Cc: andy thomas <andy@time-domain.co.uk>, freebsd-fs <freebsd-fs@freebsd.org> Subject: Re: ZFS on Hardware RAID Message-ID: <92746659-4B3F-415C-BB6A-6C99837AFAF2@sarenet.es> In-Reply-To: <CAMdBLfQvF7mXriwAvu-h5BaXBNhb_8VPRRfDmeM0u1NGoyWY_g@mail.gmail.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>
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> 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=20 as a disk. With the =E2=80=9Cvirtual JBOD=E2=80=9D you lose direct CAM = access, which means that some advanced options won=E2=80=99t be supported. For example, if you are using SSDs ZFS knows when to issue a TRIM (or, = in general, BIO_DELETE) command. Does the =E2=80=9Cvirtual JBOD=E2=80=9D offer that = option?=20 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.=20 Borja.
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