ZFS space consumption

Nuts Bastogne nutsbastogne at gmail.com
Mon May 27 09:56:10 UTC 2019

Hi All,

I'm confused about the zfs consumption of space.

I'm using ZFS to create clone from a sysprep and use it as a zvol for  vm
connected via iscsi.
The zvol has a size of 256GB.
But several dataset have a space comsuption bigger than the size of the
I thought this could be happen when we use snapshot but this is not my case.

here information from one zvol impacted :
type                  volume
volsize               256G
used                  483G
referenced            507G
copies                1
refreservation        none
compression           lz4
usedbydataset         483G
written               483G
logicalused           238G
logicalreferenced     251G

logicalused and logicalreferenced are correct, so the vm didnt see a disk
bigger than 256GB.
As used, usedbydataset, referenced properties don't include metadata
neither snapshot i dont'know what it could be.

After some research on the web some people had the same issue du to the
blocksize of their disk and had to change the ashift to 12. but this is our
configuration already.

disk : (from diskinfo -v)
 512         # sectorsize
3840755982336 # mediasize in bytes (3.5T)
7501476528   # mediasize in sectors
4096         # stripesize

volblocksize = 16k
ashift = 12

What i can check to go deeper on this issue ?
or this is just a normal behavior du to my configuration ?

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