ZVOL reservation
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Date: Sat, 20 Nov 2021 18:41:35 UTC
Hello.
Seems after years I still have doubts on how to account for space on ZFS :)
(This is on 12.2, so no OpenZFS yet)
From "man zfs":
_ refreservation = The minimum amount of space guaranteed to a dataset,
not including its descendents. When the amount of space used is below
this value, the dataset is treated as if it were taking up the amount of
space specified by refreservation.
_ usedbyrefreservation = The amount of space used by a refreservation
set on this dataset, which would be freed if the refreservation was removed.
Now:
> # zfs get all zroot/vm/sql/disk0 | grep G
> zroot/vm/sql/disk0 used 495G -
> zroot/vm/sql/disk0 available 216G -
> zroot/vm/sql/disk0 referenced 58.3G -
> zroot/vm/sql/disk0 volsize 192G local
> zroot/vm/sql/disk0 refreservation 198G local
> zroot/vm/sql/disk0 usedbysnapshots 239G -
> zroot/vm/sql/disk0 usedbydataset 58.3G -
> zroot/vm/sql/disk0 usedbyrefreservation 198G -
> zroot/vm/sql/disk0 logicalused 341G -
> zroot/vm/sql/disk0 logicalreferenced 68.9G -
I would expect:
used=max(usedbydataset,usedbyrefreservation)+usedbysnapshots=
=198+239=437G
Instead:
used=usedbydataset+usedbyrefreservation+usedbysnapshots=
=58.3+198+239=495G
IIUC, then, those 58.3G are counted twice, once as real data and once
more as reservation.
Is it so???
Given
> # zpool get all
> NAME PROPERTY VALUE SOURCE
> zroot size 896G -
> zroot capacity 72% -
> zroot altroot - default
> zroot health ONLINE -
> zroot guid 13582901126454535548 default
> zroot version - default
> zroot bootfs zroot/ROOT/default local
> zroot delegation on default
> zroot autoreplace off default
> zroot cachefile - default
> zroot failmode wait default
> zroot listsnapshots off default
> zroot autoexpand off default
> zroot dedupditto 0 default
> zroot dedupratio 1.00x -
> zroot free 246G -
> zroot allocated 650G -
> zroot readonly off -
> zroot comment - default
> zroot expandsize - -
> zroot freeing 0 default
> zroot fragmentation 53% -
> zroot leaked 0 default
> zroot bootsize - default
> zroot checkpoint - -
> zroot multihost off default
> zroot load_guid 11887969528966574378 default
> zroot feature@async_destroy enabled local
> zroot feature@empty_bpobj active local
> zroot feature@lz4_compress active local
> zroot feature@multi_vdev_crash_dump enabled local
> zroot feature@spacemap_histogram active local
> zroot feature@enabled_txg active local
> zroot feature@hole_birth active local
> zroot feature@extensible_dataset enabled local
> zroot feature@embedded_data active local
> zroot feature@bookmarks enabled local
> zroot feature@filesystem_limits enabled local
> zroot feature@large_blocks enabled local
> zroot feature@large_dnode disabled local
> zroot feature@sha512 enabled local
> zroot feature@skein enabled local
> zroot feature@device_removal disabled local
> zroot feature@obsolete_counts disabled local
> zroot feature@zpool_checkpoint disabled local
> zroot feature@spacemap_v2 disabled local
> zroot feature@allocation_classes disabled local
would a zpool upgrade help here?
Also, while we are at it:
> # zfs get all zroot | grep G
> zroot used 850G -
> zroot available 18.3G -
> zroot usedbychildren 850G -
> zroot logicalused 856G -
> # zpool get all zroot | grep G
> zroot size 896G -
> zroot free 246G -
> zroot allocated 650G -
Isn't it strange that zfs and zpool count free/available space in such a
different way?
I guess zpool does not take refreservation (in my case 200G in total)
into account.
Still 18.3+200=218, not 246G.
What does account for the difference?
bye & Thanks
av.