[OmniOS-discuss] [zfs] SSD alignment, EFI label rpool support

[Paul B. Henson]

On 8/1/2013 3:39 AM, Richard Elling wrote:

> Eh? Cylinders?
> The ZFS label already reserves 8KB of space at the front so that it will
> not clobber an SMI label.
> The actual data use begins at a 4MB offset, past the ZFS labels and
> reserved space.
>
> In other words, why would you purposefully misalign?

Well, obviously I wouldn't *purposefully* misalign, but I can't rule out 
the possibility of *incompetently* misaligning ;).

I think you are talking about the case when you give zfs an entire disk? 
In that case, yes, I understand there is no extra magic to be performed.

However, I am specifically talking about the case of the rpool, in which 
you currently cannot give zfs the entire disk, but must give it a slice 
of an SMI labeled disk.

In that case, you have the fdisk partitioning, in which from what I 
understand the Solaris partition typically starts with a one cylinder 
offset. So, when you give zfs the first slice of the Solaris partition, 
it already has an offset. Are you saying zfs refers to the fdisk 
partition, figures out where on the disk the first slice actually 
starts, and then just does the right thing? I did not believe that to be 
the case...