[zfs-discuss] Volume takes 177% of requested size
Bernd P. Ziller
bernd.ziller at dhbw-stuttgart.de
Sat Dec 27 03:06:42 EST 2014
Hi,
Am 26.12.2014 um 11:37 schrieb Uwe Sauter <uwe.sauter.de at gmail.com>:
> # 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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