On Tue, Dec 26, 2017 at 10:04 AM, O. Hartmann <ohartm...@walstatt.org> wrote:
> Am Tue, 26 Dec 2017 11:44:29 -0500 > Allan Jude <allanj...@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? > It's only necessary if your drive stupidly fails to report its physical sector size correctly, and no other FreeBSD developer has already written a quirk for that drive. Do "zdb -l /dev/adaXXXpY" for any one of the partitions in the ZFS raid group in question. It should print either "ashift: 12" or "ashift: 9". -Alan _______________________________________________ email@example.com mailing list https://lists.freebsd.org/mailman/listinfo/freebsd-current To unsubscribe, send any mail to "freebsd-current-unsubscr...@freebsd.org"