User`s guide

Memory Management

• The fsync() system call writes the modified data of a file to the hard disk. (3.7)

• Replacing devices without unmounting or otherwise disrupting access to the file system by using the

replace subcommand to btrfs, for example:

# btrfs replace failed_device replacement_device mountpoint

You do not need to unmount the file system or to stop active tasks. If the power fails during replacment,

the process resumes when the file system is next mounted. (3.8)

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

cifs

The Common Internet File System (CIFS) now provides experimental support for SMB v2, which is the

successor to the CIFS and SMB network file sharing protocols. (3.7)

ext3 and ext4

File system barriers are now enabled by default. If you experience a performance regression, you can

disable the feature by specifying the barrier=0 option to mount. (3.1)

ext4

• Store checksums of various metadata fields. Each time that a metadata field is read, the checksum of

the read data is compared with the stored checksum to detect metadata corruption. (3.5)

• Quota files are now stored in hidden inodes as file system metadata instead of as separate files in the

file system director hierarchy. Quotas are enabled as soon as the file system is mounted. (3.6)

f2fs

f2fs is an experimental file system that is optimized for flash memory storage devices and solid state drives

(SSDs). (3.8)

FUSE

The numa mount option has been added to select code paths that improve performance on NUMA

systems.

NFS

The NFS version 4.1 client supports Sessions, Directory Delegations, and parallel NFS (pNFS) as defined

in RFC 5661. pNFS can take advantage of cluster systems by providing scalable parallel access, either to

a file system or to individual files that are distributed on multiple servers. (3.7)

XFS

Journals now implement checksums for verifying log integrity. (3.8)

1.1.9 Memory Management

• The frontswap feature can store swap data is stored in transcendent memory, which is neither directly

accessible to nor addressable by the kernel. Using transcendent memory in this way can significantly

reduce swap I/O. Frontswap is so named because it can be thought of as being the opposite of a

backing store for a swap device. A suitable storage medium is a synchronous, concurrency-safe, page-