FreeBSD 9.2 Feature Highlight: ZFS General Improvements

Along with the many user facing changes discussed previously, there are also a number of internal changes to ZFS that will be available with the release of FreeBSD 9.2.

• Asynchronous destruction of datasets - ZFS will no longer make you wait while it does the house keeping to destroy a dataset and free the space that was formerly used by that dataset, the zfs command will return and the work will continue in the background
• Structural changes to the way snapshots track blocks that have changed and are no longer part of the snapshot, these changes result in higher performance when there are many snapshots and also reduce the space utilized by snapshots
• Single Copy ARC - The ZFS ARC (Adaptive Replacement Cache) is where ZFS caches data and metadata to improve performance. In previous versions of ZFS, if you accessed the same block from a dataset, and then from a clone or snapshot of that dataset, that block would end up in the ARC twice. With this improvement the block will only be stored in the ARC once allowing more unique blocks to be cached at one time
• ZIO nop-write - If your dataset has a cryptographically secure hash (SHA256) and dataset compression enabled, ZFS will now compare the checksum of the compressed block with the existing block before it is written. If the hashes match then the block is not written, saving I/O as well as reducing space consumption (if there were any snapshots of the block that would have changed, then additional space would have been consumed)
• Parallel processing of free operations - Previous versions of ZFS only used a single thread to reclaim free space. The new system now frees blocks asynchronously in parallel
• Spacemap improvements - The latest version of ZFS includes enhancements that greatly improve write performance to highly fragmented pools 
• Improved DTrace support - A number of new DTrace probes have been added to ZFS to make it easier to track what is happening inside ZFS. Additionally a new error probe has been implemented throughout ZFS that will make it easier to pinpoint the source of any error messages

In addition to the above, it is also now possible to add a comment to a zpool which is output as part of the list returned by the zpool import command.

FreeBSD 9.2 will make ZFS administration easier

On the heels of Sysadmin Appreciation Day comes news that will make every sysadmin a little bit happier. FreeBSD 9.2 is expected to be released at the end of August 2013, and with it comes a number of improvements to the administrative tools for ZFS

Below are just some of the improvements in ZFS v5000 that will be included in 9.2-RELEASE:

• zfs destroy is now capable of destroying multiple snapshots in a single command. This includes destroying a range of snapshots. In addition, the noop parameter can be used to calculate how much space will be regained by deleting one or more snapshots.
• zfs get can now accept a mount point instead of only a dataset name. This makes it easier to look up the properties of a particular dataset.
• zfs rename can now forcibly unmount the dataset from the old mount point as part of the rename, obviating the need to first forcibly unmount it with a separate command.
• zfs send now supports the noop parameter which will output the estimated size of a send operation. This is especially useful for incremental replication. This feature can be used to generate a graphical progress bar and estimate a time to completion.
• zfs send also supports a verbose parameter which will report live progress during the send operation
• zfs snapshot can now snapshot multiple datasets in a single command. Capturing snapshots of multiple file systems at the same point in time can be important to ensure consistency of backups.
• zfs list now supports a verbose argument that will display expandable space in a pool and more details about each vdev. The zfs autoexpand feature allows an array to grow if the disks are replaced with larger ones over time.
• there is also some new zfs property, logicalused and logicalreferenced report the original size of data that is stored with zfs compression

These are just some of the minor features you can look forward to with the release of FreeBSD 9.2. Watch this space for news about some of the major features of both ZFS and the main OS.