[zfs-discuss] zvol with dedupe space accounting
mikko.tanner at gmail.com
Thu Feb 25 04:37:50 EST 2016
This is because ext3 on top of zvol has no knowledge of dedup, which is
on a lower layer. ext3 "sees" 10GB of space, that's it.
Now if you were to make N number of such zvols, then you'd only reserve
the space for unique blocks _from ZFS perspective_. Each of the zvols
would still only be 10GB to ext3.
Hope this helps.
On 25.2.2016 5:32, Max Levine wrote:
> Hi All,
> It looks like deduplication is not accounted for when I have a ext3 on
> top of a deduplicated zvol. I can only write as much as the size of
> the zvol. see example:
> $ zpool create -O dedup=on tank /dev/zram0
> $ zfs create -V 10G -o volblocksize=4k tank/vol01
> $ mkfs.ext3 /dev/zvol/tank/vol01
> $ mount /dev/zvol/tank/vol01 /vol01
> $ dd if=/dev/zero of=/vol01/out bs=1G count=11
> dd: error writing /vol01/out: No space left on device
> 10+0 records in
> 9+0 records out
> 10400808960 bytes (10 GB) copied, 31.2259 s, 333 MB/s
> $ zpool list
> NAME SIZE ALLOC FREE EXPANDSZ FRAG CAP DEDUP HEALTH ALTROOT
> tank 76.5G 58.9M 76.4G - 0% 0% 1246.41x ONLINE -
> $ zfs list
> NAME USED AVAIL REFER MOUNTPOINT
> tank 10.3G 73.4G 96K /tank
> tank/vol01 10.3G 73.6G 10.1G -
> $ zfs get written tank/vol01
> NAME PROPERTY VALUE SOURCE
> tank/vol01 written 10.1G -
> Is this expected? how to take advantage of deduplication on a zvol in
> this case?
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