Date: Tue, 26 Dec 2017 18:04:44 +0100 From: "O. Hartmann" <ohartmann@walstatt.org> To: Allan Jude <allanjude@freebsd.org> Cc: freebsd-current@freebsd.org Subject: Re: ZFS: alignment/boundary for partition type freebsd-zfs Message-ID: <20171226180511.4d7d422e@thor.intern.walstatt.dynvpn.de> In-Reply-To: <bf2738b0-1774-af26-fd1e-151b6bd66c52@freebsd.org> References: <20171226172521.611a89b0@thor.intern.walstatt.dynvpn.de> <bf2738b0-1774-af26-fd1e-151b6bd66c52@freebsd.org>
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[-- Attachment #1 --] Am Tue, 26 Dec 2017 11:44:29 -0500 Allan Jude <allanjude@freebsd.org> schrieb: > On 2017-12-26 11:24, O. Hartmann wrote: > > Running recent CURRENT on most of our lab's boxes, I was in need to replace and > > restore a ZFS RAIDZ pool. Doing so, I was in need to partition the disks I was about > > to replace. Well, the drives in question are 4k block size drives with 512b emulation > > - as most of them today. I've created the only and sole partiton on each 4 TB drive > > via the command sequence > > > > gpart create -s GPT adaX > > gpart add -t freebsd-zfs -a 4k -l nameXX adaX > > > > After doing this on all drives I was about to replace, something drove me to check on > > the net and I found a lot of websites giving "advices", how to prepare large, modern > > drives for ZFS. I think the GNOP trick is not necessary any more, but many blogs > > recommend to perform > > > > gpart add -t freebsd-zfs -b 1m -a 4k -l nameXX adaX > > > > to put the partition boundary at the 1 Megabytes boundary. I didn't do that. My > > partitions all start now at block 40. > > > > My question is: will this have severe performance consequences or is that negligible? > > > > Since most of those websites I found via "zfs freebsd alignement" are from years ago, > > I'm a bit confused now an consideration performing all this days-taking resilvering > > process let me loose some more hair as the usual "fallout" ... > > > > Thanks in advance, > > > > Oliver > > > > The 1mb alignment is not required. It is just what I do to leave room > for the other partition types before the ZFS partition. > > However, the replacement for the GNOP hack, is separate. In addition to > aligning the partitions to 4k, you have to tell ZFS that the drive is 4k: > > sysctl vfs.zfs.min_auto_ashift=12 > > (2^12 = 4096) > > Before you create the pool, or add additional vdevs. > I didn't do the sysctl vfs.zfs.min_auto_ashift=12 :-(( when I created the vdev. What is the consequence for that for the pool? I lived under the impression that this is necessary for "native 4k" drives. How can I check what ashift is in effect for a specific vdev? -- O. Hartmann Ich widerspreche der Nutzung oder Übermittlung meiner Daten für Werbezwecke oder für die Markt- oder Meinungsforschung (§ 28 Abs. 4 BDSG). [-- Attachment #2 --] -----BEGIN PGP SIGNATURE----- iLUEARMKAB0WIQQZVZMzAtwC2T/86TrS528fyFhYlAUCWkKBRwAKCRDS528fyFhY lNE/AgCP/mI7TEfhdTPDYjVAny5DGWXylgPb4BpzzPcYSWBOAg+2nIdT9ySrwIq2 pLtsY9iAUqb9mmNDEVnn7LAkSQ0DAf9OdpNlKh+bcU8SAsmxNflih9NScl8djrdb 7Hsc1MFS1crG8Wwvwv8KFpZnfcPAyB6AjV3M4hKYNb+DwduO61Fu =gHOZ -----END PGP SIGNATURE-----
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