ZFS, Zvol, iSCSI and windows
Karli Sjöberg
karli.sjoberg at slu.se
Fri Sep 25 11:13:45 UTC 2015
fre 2015-09-25 klockan 11:08 +0200 skrev 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?
>
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Is it this effect you are seeing:
https://forums.freebsd.org/threads/mitigating-4k-disk-issues-on-raidz.37365/
/K
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