gptzfsboot and 4k sector raidz

[Daniel Mayfield]

>> I noticed that the free data space was also bigger.  I tried it with
>> raidz on the 512B sectors and it claimed to have only 5.3T of space.
>> With 4KB sectors, it claimed to have 7.25T of space.  Seems like
>> something is wonky in the space calculations?
> 
> Hmmmm.  It didn't occur to me that the space calculations might be wonky.  That could explain why I was seeing disk usage much higher on 4K than 512-bytes for all my zfs datasets.  Here's my zpool/zfs output w/ 512-byte sectors (4-disk raidz):
> 
> [root at flanker/ttypts/0(~)#] zpool list tank
> NAME   SIZE  ALLOC   FREE    CAP  DEDUP  HEALTH  ALTROOT
> tank  7.12T   698G  6.44T     9%  1.16x  ONLINE  -
> [root at flanker/ttypts/0(~)#] zfs list tank
> NAME   USED  AVAIL  REFER  MOUNTPOINT
> tank   604G  4.74T  46.4K  legacy
> 
> It's a raidz1-0 of four 2TB disks, so the space available should be (4-1=3)*2TB=6TB?  Although I presume that's 6-marketing-terabtyes, which translates to ... 6000000000000/(1024^4)=5.  And I've got 64k boot, 8G swap, 16G scratch on each drive *before* the tank, so eh, I guess 4.74T sounds about right.
> 
> The 7.12T reported by zpool doesn't seem to be taking into account the reduced space from the raidz parity.  *shrug*
> 
> Enough about sizes; what's your read/write performance like between 512-byte/4K?  I didn't think to test performance in the 4K configuration; I really wish I had, now.

I didn't test performance.  I'm doing all the work running from the mfsBSD boot disc.  I'm not sure a simple 'dd' is a good test, but if you have suggestions, I'm open.

daniel