User`s guide

File Systems

• Switching from tree locks to reader/writer locks improves the performance of read and write-intensive

workloads. (3.1)

• Performance improvements in several areas, particularly for random write workloads. (3.2)

• Allowing overcommit of ENOSPC reservations to improve performance. (3.2)

• Add automatic backup of superblock information about tree roots for the previous 4 commits. Add the -o

recovery mount option to enable use the root history log if required. (3.2)

• Add code to follow back references, replacing the manual process for walking those references, and

including more detailed corruption messages. (3.2)

• Allow user-space utilities to inspect metadata. (3.2)

• Improve performance of checksum verification of read-aheads. (3.2)

• Add the nospace_cache mount option to disable cache loading without clearing the cache. (3.2)

• Improve performance of committing transactions. (3.2)

• When mounting a subvolume, allow a path relative to the tree root to be specified to -o subvol. (3.2)

• Rework the logic for cluster allocation. (3.3)

• Rewrite the block group trimming code. (3.3)

• Increase the size of system chunks. (3.3)

• Remove caching code that caused unnecessary fragmentation and complexity. (3.4)

• Remove the code to silently switching single chunks to RAID-0 when balancing a file system. The

restriper now allows a choice of RAID-0 or concatenation. (3.4)

• Support metadata blocks that are larger than 4 KB. (3.5)

• The thread_pool size can be changed at remount time. (3.5)

• Add the DEVICE_READY ioctl() to be used in conjunction with btrfs device ready device,

providing a lightweight method of telling if all the devices required for a file system are currently in the

cache. (3.6)

• Allow compression to be disabled by specifying the compress=no mount option. (3.6)

• Improve multithread buffer reads. (3.6)

• Support UUIDs for subvolumes, and introduce ctime, otime, stime, and rtime for subvolumes,

including a transid for each time. (3.6)

• Rework the DEV_STATS ioctl() to allow it to either get or reset device statistics depending on the

argument specified. (3.6)

• Make the compress and nodatacow mount options mutually exclusive. To improve O_SYNC

performance, asynchronous metadata checksumming is not performed under some circumstances. (3.7)

For more information, see https://btrfs.wiki.kernel.org/index.php/Changelog.

cifs

• Add UID/GID to SID mapping. (3.2)