[zfs-discuss] Volume takes 177% of requested size

UbuntuNewbie chessdoter at googlemail.com
Sat Dec 27 19:15:05 EST 2014


Thank you for this explanation (and convincing example).

During my tests, i found volume snapshots do in fact NOT use up volsize any 
longer. My experiences came from several years back, when ZoL still had no 
production ready stable release. - Apologies for the confusion, that i may 
have caused. (to anyone reading along)

Am Samstag, 27. Dezember 2014 09:06:44 UTC+1 schrieb Bernd P. Ziller:
>
> Hi, 
>
> Am 26.12.2014 um 11:37 schrieb Uwe Sauter <uwe.sa... at gmail.com 
> <javascript:>>: 
>
> > # zfs create storage/Backup/disk -b 512 -V 1953514584k 
> > 
> > and then dd'ed the disk to the volume 
> > 
> > # dd if=/dev/sdo of=/dev/zvol/storage/Backup/disk bs=8M iflag=direct 
>
> It's the zvols blocksize of 512 bytes and the resulting metadata overhead. 
> (Plus the write overhead for raidz?) 
> I guess someone with deeper insight can explain this further. :) 
>
> Just did a test with two 2G zvols with 512 and 8192 bytes blocksize: 
>
> # zfs create tank/v512 -b 512 -V 2G 
> # zfs create tank/v8192 -b 8192 -V 2G 
>
> # dd if=/dev/urandom bs=8k of=/dev/tank/v8192 
> # dd if=/dev/tank/v8192 bs=8k of=/dev/tank/v512 
>
> # zfs get all tank/v512 | grep G 
> NAME       PROPERTY              VALUE                 SOURCE 
> tank/v512  used                  3,60G                 - 
> tank/v512  referenced            3,60G                 - 
> tank/v512  volsize               2G                    local 
> tank/v512  refreservation        3,01G                 local 
> tank/v512  usedbydataset         3,60G                 - 
> tank/v512  written               3,60G                 - 
> tank/v512  logicalused           2,19G                 - 
> tank/v512  logicalreferenced     2,19G                 - 
> # zfs get all tank/v8192 | grep G 
> NAME        PROPERTY              VALUE                 SOURCE 
> tank/v8192  used                  2,06G                 - 
> tank/v8192  referenced            2,02G                 - 
> tank/v8192  volsize               2G                    local 
> tank/v8192  refreservation        2,06G                 local 
> tank/v8192  usedbydataset         2,02G                 - 
> tank/v8192  written               2,02G                 - 
> tank/v8192  logicalused           2,01G                 - 
> tank/v8192  logicalreferenced     2,01G                 - 
>
> -- 
>
>

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