How to reserve space in ZFS pool for Proxmox Backup Server?

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pvpaulo

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Jun 15, 2022
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Good afternoon everyone.
I'm having a space issue with the Proxmox backup server.
I have a simple ZFS pool without RAID.
I added some disks to this pool.
Backups are working correctly.
However, because the client's environment is large, sometimes garbage collection takes a long time to complete, and sometimes the pool itself runs out of space.
To manage or run garbage collection manually, I add a new disk to the pool to free up space, and I can run garbage collection correctly.

Is there a suitable configuration I can use to reserve at least 50GB of this pool to avoid writing anything?
This way, if garbage collection fails or if the client adds more machines for backup, even if the pool fills up, I have those 50GB to use and run garbage collection manually or clean up without needing to add another disk to the pool and extend it.
I'm using ZFS.
I'll send the output and status of my pool as an example:

1758814333585.png
 
A just striped pool with 5 hdd ? I hope you have a good working backup and restore solution and good couple of time for next hdd defect available !!
:)
 
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[TUTORIAL] Post in thread 'Protect a PBS datastore on ZFS, so that it does not become completely full'

I use zfs create -o reservation=100G pool/.reserved-space and also monitor the space usage.
If you have an emergency, as in the space is full, and forgot to do that before then temporarily altering spa_slop_shift might help.
For example
Bash: 
# Shows current value. Default is 5
cat /sys/module/zfs/parameters/spa_slop_shift

echo 6 > /sys/module/zfs/parameters/spa_slop_shift
Increase the value if needed. Make sure to revert this to the default/previous value when done.

Here's an example of the reserved percentage you get with different values
Code: 
1:  50.000
2:  25.000
3...
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