Introduction
In the context of using multiple ZFS datasets on one pool backed by HDDs, storing backups, and forwarding backups using RSYNC pools with different HDDs, the question arises about the effect of changing ZFS properties using XATTR (Extended Attributes). This article aims to provide a detailed context on this topic, covering key concepts, subtopics, and examples.
ZFS Datasets
ZFS datasets are logical volumes managed by the ZFS file system. Each dataset is a separate file system with its own properties, permissions, and mount points. ZFS allows you to create multiple datasets within a single pool, making it an ideal solution for managing backups and forwarding backups using RSYNC.
Changing ZFS Properties
ZFS properties can be modified using the zfs set command. These properties control various aspects of the dataset, such as compression, recordsize, and atime.
XATTR Changes
XATTR (Extended Attributes) are key-value pairs that can be attached to files and directories in ZFS. They provide an additional layer of metadata that can be used to store custom information. Changing an XATTR using the setxattr command takes immediate effect without requiring a dataset rewrite.
ZFS Property vs. XATTR
While both ZFS properties and XATTR can be modified without a dataset rewrite, they serve different purposes. ZFS properties are internal dataset properties that control various aspects of the dataset, while XATTR are user-defined metadata that can be attached to files and directories.
Effect on Backups
When changing ZFS properties or XATTR, it's essential to understand the impact on backups. If you're using RSYNC to forward backups to another pool, changing a property or XATTR on the source pool will not immediately affect the backup. However, the next RSYNC sync will propagate the change to the target pool.
Example
Let's consider an example where we have two datasets, datasets/src and datasets/dest, on separate HDDs within the same pool. We'll change the compression property of the datasets/src dataset using the zfs set command:
# zfs set compression=lz4 datasets/src
This change takes immediate effect on the datasets/src dataset but does not affect the datasets/dest dataset until the next RSYNC sync.
Conclusion
In conclusion, changing ZFS properties and XATTR takes immediate effect on the affected dataset but may not propagate to other datasets or backups until the next RSYNC sync. Understanding the behavior of ZFS properties and XATTR is crucial when managing backups and forwarding them using RSYNC.