Re: [zfs-discuss] ZVOL vs regular fs — huge difference in data consumption

Daniel Smedegaard Buus danielbuus at gmail.com
Fri May 17 11:44:33 EDT 2013


Hi Gregor, thanks for responding :)

On Fri, May 17, 2013 at 5:30 PM, Gregor Kopka <gregor at kopka.net> wrote:

>  Try -s when creating the ZVOL, else it won't be sparse and allocate the
> whole 'disk' upfront (see also the comment about quickformat).
>
>
I used -o refreservation=0 to do that. Does it do the same thing?


>  Plus you'll have the overhead ZFS needs to enable its magic, this will be
> the 4.5G extra.
>
>
But it's not 4.5G extra, is 12GB extra compared to the regular fs.


>  Here's a zfs get all of a sparse zvol shared over iscsi to a client as
> boot disk, containing a fresh windows 7 base install plus updates:
>
> NAME               PROPERTY              VALUE                  SOURCE
> data/iscsi/master  type                  volume                 -
> data/iscsi/master  creation              Thu Mar 21 16:07 2013  -
> data/iscsi/master  used                  30.6G                  -
> data/iscsi/master  available             878G                   -
> data/iscsi/master  referenced            22.4G                  -
> data/iscsi/master  compressratio         1.02x                  -
> data/iscsi/master  reservation           none                   default
> data/iscsi/master  volsize               80G                    local
> data/iscsi/master  volblocksize          8K                     -
> data/iscsi/master  checksum              on                     default
> data/iscsi/master  compression           lz4                    inherited
> from data/iscsi
> data/iscsi/master  readonly              off                    default
> data/iscsi/master  copies                1                      default
> data/iscsi/master  refreservation        none                   default
> data/iscsi/master  primarycache          all                    default
> data/iscsi/master  secondarycache        all                    default
> data/iscsi/master  usedbysnapshots       8.15G                  -
> data/iscsi/master  usedbydataset         22.4G                  -
> data/iscsi/master  usedbychildren        0                      -
> data/iscsi/master  usedbyrefreservation  0                      -
> data/iscsi/master  logbias               latency                default
> data/iscsi/master  dedup                 off                    default
> data/iscsi/master  mlslabel              none                   default
> data/iscsi/master  sync                  always                 inherited
> from data/iscsi
> data/iscsi/master  refcompressratio      1.02x                  -
> data/iscsi/master  written               0                      -
> data/iscsi/master  snapdev               hidden                 default
>
>
I just did a similar install of Windows 7 Ultimate, except my ZVOL is 7.4
GB ;) Good tip for that: use something like CCleaner or the MS tool to zero
out free disk space before snapshotting. Shaves the storage space used down
immensely! Especially when defrag is completely turned off.
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