ZFS, Zvol, iSCSI and windows
Willem Jan Withagen
wjw at digiware.nl
Fri Sep 25 09:08:37 UTC 2015
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?
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