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

Daniel Smedegaard Buus danielbuus at gmail.com
Fri May 17 11:05:10 EDT 2013

Hi :)

I have this bunch of small sample files (50+ gigs worth) that I've
previously shared via NFS to my Hackintosh where I play around with making

The FS I created for it is a regular zfs one, just with gzip-9 compression
added to the mix.

The zpool is quite massive, so my recordsize is 128k, which I've assumed
meant that I was wasting a bunch of space on smaller files. But now I'm not
so sure.

I've been playing around with SCST and ZVOLs and wanted to move all these
samples onto a ZVOL formatted with NTFS (4k sectors) (so I can also mount
it in Windows). I created the zvol with gzip-9 compression as well, and I
was kind of expecting to see the end result being less space consumed than
with the regular ZFS fs.

Not so. In fact, I created this ZVOL with -V 60G, but references,
usedbydataset, and written all say 64.5 GB, whereas the regular ZFS FS uses
52.6 GB.

What am I missing here? Probably a lot, so if you can, please educate me! I
just don't get it!

My properties on the zvol and filesystem:

NAME                   PROPERTY              VALUE                  SOURCE
titanic/zvol-composer  type                  volume                 -
titanic/zvol-composer  creation              Sun May 12 11:56 2013  -
titanic/zvol-composer  used                  64.5G                  -
titanic/zvol-composer  available             343G                   -
titanic/zvol-composer  referenced            64.5G                  -
titanic/zvol-composer  compressratio         1.05x                  -
titanic/zvol-composer  reservation           none                   default
titanic/zvol-composer  volsize               60G                    local
titanic/zvol-composer  volblocksize          32K                    -
titanic/zvol-composer  checksum              on                     default
titanic/zvol-composer  compression           gzip-9                 local
titanic/zvol-composer  readonly              off                    default
titanic/zvol-composer  copies                1                      default
titanic/zvol-composer  refreservation        none                   local
titanic/zvol-composer  primarycache          all
 inherited from titanic
titanic/zvol-composer  secondarycache        all                    default
titanic/zvol-composer  usedbysnapshots       0                      -
titanic/zvol-composer  usedbydataset         64.5G                  -
titanic/zvol-composer  usedbychildren        0                      -
titanic/zvol-composer  usedbyrefreservation  0                      -
titanic/zvol-composer  logbias               latency                default
titanic/zvol-composer  dedup                 off                    default
titanic/zvol-composer  mlslabel              none                   default
titanic/zvol-composer  sync                  standard               default
titanic/zvol-composer  refcompressratio      1.05x                  -
titanic/zvol-composer  written               64.5G                  -
titanic/zvol-composer  snapdev               hidden                 default

NAME                 PROPERTY              VALUE                  SOURCE
titanic/Systems/Dex  type                  filesystem             -
titanic/Systems/Dex  creation              Wed Apr 24 19:07 2013  -
titanic/Systems/Dex  used                  52.6G                  -
titanic/Systems/Dex  available             343G                   -
titanic/Systems/Dex  referenced            52.6G                  -
titanic/Systems/Dex  compressratio         1.07x                  -
titanic/Systems/Dex  mounted               yes                    -
titanic/Systems/Dex  quota                 none                   default
titanic/Systems/Dex  reservation           none                   default
titanic/Systems/Dex  recordsize            128K                   default
titanic/Systems/Dex  mountpoint            /titanic/Systems/Dex   inherited
from titanic
titanic/Systems/Dex  sharenfs              off                    inherited
from titanic
titanic/Systems/Dex  checksum              on                     default
titanic/Systems/Dex  compression           gzip-9                 local
titanic/Systems/Dex  atime                 off                    inherited
from titanic
titanic/Systems/Dex  devices               on                     default
titanic/Systems/Dex  exec                  on                     default
titanic/Systems/Dex  setuid                on                     default
titanic/Systems/Dex  readonly              off                    default
titanic/Systems/Dex  zoned                 off                    default
titanic/Systems/Dex  snapdir               hidden                 default
titanic/Systems/Dex  aclinherit            restricted             default
titanic/Systems/Dex  canmount              on                     default
titanic/Systems/Dex  xattr                 on                     default
titanic/Systems/Dex  copies                1                      default
titanic/Systems/Dex  version               4                      -
titanic/Systems/Dex  utf8only              off                    -
titanic/Systems/Dex  normalization         none                   -
titanic/Systems/Dex  casesensitivity       sensitive              -
titanic/Systems/Dex  vscan                 off                    default
titanic/Systems/Dex  nbmand                off                    default
titanic/Systems/Dex  sharesmb              off                    default
titanic/Systems/Dex  refquota              none                   default
titanic/Systems/Dex  refreservation        none                   default
titanic/Systems/Dex  primarycache          all                    inherited
from titanic
titanic/Systems/Dex  secondarycache        all                    default
titanic/Systems/Dex  usedbysnapshots       0                      -
titanic/Systems/Dex  usedbydataset         52.6G                  -
titanic/Systems/Dex  usedbychildren        0                      -
titanic/Systems/Dex  usedbyrefreservation  0                      -
titanic/Systems/Dex  logbias               latency                default
titanic/Systems/Dex  dedup                 off                    default
titanic/Systems/Dex  mlslabel              none                   default
titanic/Systems/Dex  sync                  standard               default
titanic/Systems/Dex  refcompressratio      1.07x                  -
titanic/Systems/Dex  written               52.6G                  -
titanic/Systems/Dex  snapdev               hidden                 default
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