ZFS, Zvol, iSCSI and windows

[Willem Jan Withagen]

Hi,

Because of the Network Video Recorder (on windows) we use only likes 
"real" disks, and not SMB disks. We started using ZVOLs which are 
exported thru iSCSI/ctld....

And that works really well, so there all thumbs up for this combo.

However..... (you knew that was coming)
I do have some questions, and hope somebody can share some insights.

1)
This is a ZFS question.

I have created a ZVOL with:
	zfs create -s -V 5T zfsraid/nvr2

Looking at the disk usage in 'zfs get all':
NAME          PROPERTY              VALUE                  SOURCE
zfsraid/nvr2  used                  9.97T                  -
zfsraid/nvr2  available             438G                   -
zfsraid/nvr2  referenced            9.97T                  -
zfsraid/nvr2  compressratio         1.00x                  -
zfsraid/nvr2  reservation           none                   default
zfsraid/nvr2  volsize               5T                     local
zfsraid/nvr2  volblocksize          8K                     -
zfsraid/nvr2  checksum              on                     default
zfsraid/nvr2  compression           lz4                    default
zfsraid/nvr2  primarycache          all                    default
zfsraid/nvr2  secondarycache        all                    default
zfsraid/nvr2  usedbysnapshots       0                      -
zfsraid/nvr2  usedbydataset         9.97T                  -
zfsraid/nvr2  usedbychildren        0                      -
zfsraid/nvr2  usedbyrefreservation  0                      -
zfsraid/nvr2  sync                  standard               default
zfsraid/nvr2  written               9.97T                  -
zfsraid/nvr2  logicalused           4.97T                  -
zfsraid/nvr2  logicalreferenced     4.97T                  -
zfsraid/nvr2  volmode               default                default

And what sort of "worries" me is that it seems that this volume is using 
twice the amount of diskspace it is offering as ZVOL?

a) Is this really true?
b) Should I have done something different to not waste so much overhead?

Note that the compression rate is 1.00x, which is of course due to 
writing h264 media streams that do not compress at all. But is the 
parents default, and I haven't turned it off.

2)
The second one might be more a Windows question, but anyways.

The export is that same 5T ZVOL, plain create with
	zfs create -s -V 5T zfsraid/nvr2
Under Windows I used the regular stuff to format the dis with GPT and 
NTFS with 8k segments. (matching the ZVOL blocksize)

Upon reboot FreeBSD notices the following:
GEOM_PART: partition 1 on (zvol/zfsraid/nvr2, GPT) is not aligned on
	8192 bytes	
By itself not technical problem. But the warning does hint that the 
alignment is thus, that performance might suffer. the backing disks are 
WD REDs which are 4K sectors.... So the misalignment could cause too 
many read/writes for writing.

Does anybody have a clue as how to get Windows to do the aligning correctly?