Features of the BTRFS Filesystem

Copy-on-write Mechanism:

BTRFS employs a copy-on-write approach, ensuring that when modifications are needed in a file, the filesystem doesn't alter the file in its current location. Instead, changes are written to a different location. This strategy minimizes issues related to "partial" writes that often occur during power failures, where the original data is deleted, but the new data hasn't been written yet. From a recovery perspective, copy-on-write enhances the likelihood of successful recovery. Even if the latest file metadata is damaged, previous versions are likely to exist on the device.

Checksums for Data and Metadata:

BTRFS calculates checksums for both metadata and user data. This feature allows the filesystem to detect errors in the structure and rectify them. For instance, if the checksum calculation during a read operation reveals a mismatch in a data block, BTRFS attempts to locate a valid copy of the block and correct the error, particularly if mirroring is enabled.

Online Data Scrubbing:

Linked to checksums, BTRFS employs online data scrubbing, periodically checking the filesystem structure for errors and correcting them. This proactive approach enhances the integrity of the filesystem.

Built-in Compression:

BTRFS offers optional transparent compression utilizing ZLIB DEFLATE or LZO algorithms. This feature allows for efficient storage utilization.

In-place Conversion from ext3/4 to BTRFS:

BTRFS provides a specialized tool for in-place conversion from ext3/4 to BTRFS. During this conversion, ext filesystem metadata remains unaltered, and BTRFS writes its metadata to available free space. This cautious process ensures that data on the device remains unaffected even if a failure occurs during conversion. Moreover, users can interrupt the "changing filesystem type" operation at any point. Once the conversion is complete, access is granted to all files and folders created on ext.

Future Implications:

It's plausible that in the future, NAS devices might automatically convert their filesystems to BTRFS during firmware updates. Users may not be explicitly notified, considering NAS devices are often perceived as sealed units not intended for user servicing.