Date: Mon, 29 Jun 2015 10:29:36 -0400 From: Paul Kraus <paul@kraus-haus.org> To: freebsd-questions <freebsd-questions@freebsd.org> Subject: Re: Corrupt GPT on ZFS full-disks that shouldn't be using GPT Message-ID: <A11C7102-5B07-4301-856A-908F6D2A7A65@kraus-haus.org> In-Reply-To: <alpine.BSF.2.20.1506290815150.85919@wonkity.com> References: <CAPi0psvpvO4Kpbietpzyx1TjyB20hWV%2BCK-y3bWG4OARE1VMSg@mail.gmail.com> <alpine.BSF.2.20.1506280019400.14091@wonkity.com> <CAPi0psv7io6dhqbNxm6gp%2BW1npmNoU1agF%2Bt=7aEteNmpzqJXQ@mail.gmail.com> <alpine.BSF.2.20.1506281526030.60581@wonkity.com> <5590A7AE.9040303@sneakertech.com> <alpine.BSF.2.20.1506290815150.85919@wonkity.com>
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On Jun 29, 2015, at 10:19, Warren Block <wblock@wonkity.com> wrote: > On Sun, 28 Jun 2015, Quartz wrote: >=20 >>> Remember, ZFS >>> leaves space unused at the end of a disk to allow for variations in >>> nominal disk size. >>=20 >> Holy what the heck, no it doesn't! One big issue with zfs is that you = CANNOT shrink a pool's size once it's been created, for any reason. You = can't remove vdevs, and any replacement disk must bigger or exactly = equal in size; even a disk with one less sector and you're SOL. This is = my biggest gripe with zfs by far and in fact I just asked freebsd-fs = about this less than a week ago wondering if it had been addressed = finally (it hasn't). I do recall a change in ZFS behavior to leave a very small amount of = space unused at the every end of the drive to account for the = differences in real sizes between various vendors drives that were = nominally the same size. This only applied if you used the entire disk = and did not use any partitioning. This was in both the Solaris and = OpenSolaris versions of ZFS, so it predates the fork of the ZFS code. I have had no issues using disks of different manufacturers and even = models within manufacturers (which sometimes do vary in size by a few = blocks) as long as they were all the same nominal size (1 TB or 500 GB = in my case) and I had handed the entire disk to ZFS and not a partition. This is NOT an indication of any sort that you can shrink an existing = zpool nor does it imply that any given zpool is not writing to certain = blocks at the end of the disk, but that the space allocated by the zpool = create, when using an entire disk, leaves a little bit of wiggle room at = the end that is NOT part of the zpool. I will see if I can dig up the documentation on this. Note that it is a = very small amount as drives of the same nominal capacity vary very = little in real capacity. -- Paul Kraus paul@kraus-haus.org
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