Re: [CFT] Patch to bsdinstall to support root-on-ZFS and GELI

On 10/08/13 22:25, Freddie Cash wrote:
> On Tue, Oct 8, 2013 at 1:17 PM, Nathan Whitehorn
> <nwhitehorn_at_freebsd.org <mailto:nwhitehorn_at_freebsd.org>>wrote:
>
>     4. What is this gnop stuff for?
>
>
> Can't comment on the rest, but gnop is required to create 4K-aligned
> vdevs where the minimum block size is 4K (aka ashift=12).  Without
> this, ZFS relies on the underlying disk driver providing the correct
> information, and most don't.  Also, if you don't do this, and create a
> vdev using 512B sectors, the ashift will be set to 9, and replacing
> the drive down the line with 4K Advanced Format drive will drop your
> drive performance in the toilet.​​
>
> Thus, to future-proof your pool, you need to:
>   - set the ashift of the pool to 12 (4 KB)
>   - align the disk/partition on 4 KB boundaries (starting partition at
> 1 MB works well)
>
> Until our ZFS gains the ability to set a minimum ashift for the pool,
> or to set the ashift at vdev creation, or all drive manufacturers
> write perfect firmware, than we need to fake it with gnop.
>

Well, that's a disgusting hack, but I see why it's there. Thanks for the
explanation!
-Nathan