Zfs terms

To decrease the size of a ZFS volume using OpenZFS, you typically need to perform the following steps:

Backup Data: Before resizing any volume, it's crucial to back up your data to prevent any potential data loss.
Unmount the Filesystem: Make sure the filesystem is unmounted to prevent data corruption during the resizing process.
Reduce the Volume Size: Use the zfs set command to set the new size for the ZFS volume. You can specify the new size using the -V flag followed by the desired size.
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sudo zfs set volsize=new_size <pool_name>/<volume_name>
Replace new_size with the desired size for the volume, and <pool_name>/<volume_name> with the name of the ZFS volume you want to resize.
Resize the Filesystem: After resizing the volume, you need to resize the filesystem to match the new size. Use the appropriate command for your filesystem type. For example, if you're using ZFS as the filesystem:
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sudo zpool set autoexpand=on <pool_name>
sudo zpool online -e <pool_name> <device>
Replace <pool_name> with the name of your ZFS pool and <device> with the device name of the ZFS volume you resized.
Remount the Filesystem: Once the volume and filesystem have been resized, remount the filesystem to make it accessible again.
Verify: Double-check that the volume has been resized successfully and that your data is intact.
Always ensure you have a backup before performing any operations that could potentially result in data loss. Resizing volumes can be risky, so it's essential to understand the implications and proceed with caution.

User
openzfs vs USED  AVAIL     REFER
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In OpenZFS, the output of the zfs list command typically includes several columns, including USED, AVAIL, and REFER, which provide information about storage usage within ZFS datasets. Here's what each of these columns represents:

USED: This column shows the amount of space currently in use within the dataset and any of its children (snapshots, clones, etc.). It includes both data stored within the dataset and any associated metadata. The value is reported in bytes.
AVAIL: This column displays the amount of space available for use within the dataset. It represents the amount of unused space within the dataset, which can be allocated for storing new data. The value is reported in bytes.
REFER: This column represents the amount of data that is referenced by the dataset and any of its children. It includes the size of the dataset itself as well as any snapshots or clones based on the dataset. Unlike the USED column, the REFER column does not include the size of any shared data between snapshots or clones. The value is reported in bytes.
In summary:

USED: Total space used by the dataset and its children.
AVAIL: Available space within the dataset for storing new data.
REFER: Total size of the dataset and its children, including snapshots and clones, but excluding shared data.
These columns provide valuable insights into how storage space is being utilized within ZFS datasets, helping administrators monitor storage consumption and plan for future capacity requirements.