followup storage question
allan at physics.umn.edu
Fri Sep 11 15:27:47 UTC 2015
On 9/11/2015 7:59 AM, William A. Mahaffey III wrote:
> The Wiki page https://wiki.freebsd.org/RootOnZFS/GPTZFSBoot/9.0-RELEASE
> illustrates using gnop to enforce 4K alignment of gpt partitions for
> subsequent use by ZFS. However the gpart commands also use the '-a 4k'
> arguments, aligning partitions on 4k boundaries as I understand things.
> Is the gnop command also necessary ? TIA & have a nice weekend.
My experience is I only ever install on smaller devices so never really
worry about 4k alignment at that time, only for making large storage
pools later. With that mind mind here is my "easy" answer for 9.3 and
10.x. The installer "auto ZFS" has a 4k alignment option which I would
assume works as advertised (having said that it would be simple to do a
basic install and then examine that to confirm). For making subsequent
pools, I simply set vfs.zfs.min_auto_ashift=12 is /etc/sysctl.conf,
after which you will get 4k block alignment without messing with gnop.
On 9.1 you had to do the gnop tricks but 9.3 supports the auto_ashift
On 9.3+, "zpool status" also *tells you* if you got the block alignment
wrong, which is a big help over 9.1 where it could lurk undetected!
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