Difference between revisions of "File systems"
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Revision as of 21:12, 12 February 2014
- A file system (or filesystem) is a means to organize data expected to be retained after a program terminates by providing procedures to store, retrieve and update data, as well as manage the available space on the device(s) which contain it. A file system organizes data in an efficient manner and is tuned to the specific characteristics of the device.
Individual drive partitions can be setup using one of the many different available filesystems. Each has its own advantages, disadvantages, and unique idiosyncrasies. A brief overview of supported filesystems follows; the links are to wikipedia pages that provide much more information.
Before being formatted, a drive should be partitioned.
Type of file systems
- Btrfs - Also known as "Better FS", is a new filesystem with powerful features similar to Sun/Oracle's excellent ZFS. These include snapshots, multi-disk striping and mirroring (software RAID without mdadm), checksums, incremental backup, and on-the-fly compression that can give a significant performance boost as well as save space. As of January 2011, Btrfs is considered unstable although it has been merged into the mainline kernel with an experimental status. Btrfs appears to be the future of GNU/Linux filesystems and is offered as a root filesystem option in all major distribution installers.
- exFAT - Microsoft file system optimized for flash drives. Unlike NTFS, exFAT cannot pre-allocate disk space for a file by just marking arbitrary space on disk as 'allocated'. As in FAT, when creating a file of known length, exFAT must perform a complete physical write equal to the size of the file.
- ext2 - Second Extended Filesystem is an established, mature GNU/Linux filesystem that is very stable. A drawback is that it does not have journaling support or barriers. Lack of journaling can result in data loss in the event of a power failure or system crash. It may also be not convenient for root (
/homepartitions because file-system checks can take a long time. An ext2 filesystem can be converted to ext3.
- ext3 - Third Extended Filesystem is essentially the ext2 system with journaling support and write barriers. It is backward compatible with ext2, well tested, and extremely stable.
- ext4 - Fourth Extended Filesystem is a newer filesystem that is also compatible with ext2 and ext3. It provides support for volumes with sizes up to 1 exabyte (i.e. 1,048,576 terabytes) and files sizes up to 16 terabytes. It increases the 32,000 subdirectory limit in ext3 to 64,000. It also offers online defragmentation capability.
- F2FS - Flash-Friendly File System is a flash file system created by Kim Jaegeuk (Hangul: 김재극) at Samsung for the Linux operating system kernel. The motivation for F2FS was to build a file system that from the start takes into account the characteristics of NAND flash memory-based storage devices (such as solid-state disks, eMMC, and SD cards), which have been widely being used in computer systems ranging from mobile devices to servers.
- JFS - IBM's Journaled File System was the first filesystem to offer journaling. It had many years of development in the IBM AIX® operating system before being ported to GNU/Linux. JFS makes the smallest demand on CPU resources of any GNU/Linux filesystem. It is very fast at formatting, mounting, and filesystem checks (fsck). JFS offers very good all-around performance especially in conjunction with the deadline I/O scheduler. It is not as widely supported as the ext series or ReiserFS, but still very mature and stable.
- NILFS2 - New Implementation of a Log-structured File System was developed by NTT. It records all data in a continuous log-like format that is only appended to and never overwritten. It is designed to reduce seek times and minimize the type of data loss that occurs after a crash with conventional Linux filesystems.
- NTFS - File system used by Windows. NTFS has several technical improvements over FAT and HPFS (High Performance File System), such as improved support for metadata, and the use of advanced data structures to improve performance, reliability, and disk space utilization, plus additional extensions, such as security access control lists (ACL) and file system journaling.
- Reiser4 - Successor to the ReiserFS file system, developed from scratch by Namesys and sponsored by DARPA as well as Linspire, it uses B*-trees in conjunction with the dancing tree balancing approach, in which underpopulated nodes will not be merged until a flush to disk except under memory pressure or when a transaction completes. Such a system also allows Reiser4 to create files and directories without having to waste time and space through fixed blocks.
- ReiserFS - Hans Reiser's high-performance journaling FS (v3) uses a very interesting method of data throughput based on an unconventional and creative algorithm. ReiserFS is touted as very fast, especially when dealing with many small files. ReiserFS is fast at formatting, yet comparatively slow at mounting. Quite mature and stable. ReiserFSv3 is not being actively developed at this time. Generally regarded as a good choice for
- Swap - Filesystem used for swap partitions.
- VFAT - Virtual File Allocation Table is technically simple and supported by virtually all existing operating systems. This makes it a useful format for solid-state memory cards and a convenient way to share data between operating systems. VFAT supports long file names.
- XFS - Early journaling filesystem originally developed by Silicon Graphics for the IRIX operating system and ported to GNU/Linux. It provides very fast throughput on large files and filesystems and is very fast at formatting and mounting. Comparative benchmark testing has shown it to be slower when dealing with many small files. XFS is very mature and offers online defragmentation capability.
- ZFS - Combined file system and logical volume manager designed by Sun Microsystems. The features of ZFS include protection against data corruption, support for high storage capacities, integration of the concepts of filesystem and volume management, snapshots and copy-on-write clones, continuous integrity checking and automatic repair, RAID-Z and native NFSv4 ACLs.
All the above filesystems with the exception of ext2, FAT16/32, use journaling. Journaling provides fault-resilience by logging changes before they are committed to the filesystem. In the event of a system crash or power failure, such file systems are faster to bring back online and less likely to become corrupted. The logging takes place in a dedicated area of the filesystem.
Not all journaling techniques are the same. Only ext3 and ext4 offer data-mode journaling, which logs both data and meta-data. Data-mode journaling comes with a speed penalty and is not enabled by default. The other filesystems provide ordered-mode journaling, which only logs meta-data. While all journaling will return a filesystem to a valid state after a crash, data-mode journaling offers the greatest protection against corruption and data loss. There is a compromise in system performance, however, because data-mode journaling does two write operations: first to the journal and then to the disk. The trade-off between system speed and data safety should be considered when choosing the filesystem type.
Arch Linux support
- btrfs-progs — Btrfs support.
- dosfstools — VFAT support.
- exfat-utils — exFAT support.
- f2fs-tools — F2FS support.
- fuse-exfat — exFAT mount support.
- jfsutils — JFS support.
- nilfs-utils — NILFS support.
- ntfs-3g — NTFS support.
- reiser4progs — ReiserFSv4 support.
- reiserfsprogs — ReiserFSv3 support.
- util-linux — Swap support.
- xfsprogs — XFS support.
- zfs — ZFS support.
- http://zfsonlinux.org/ || AUR
- zfs-fuse — ZFS support via FUSE.
- http://zfs-fuse.net/ || AUR
Format a device
Before starting, you need to know which name Linux gave to your device. Hard drives and USB sticks show up as
/dev/sdx, where x is a lowercase letter, while partitions show up as
/dev/sdxY, where Y is a number.
If the device you want to format is mounted, it will show up in the MOUNTPOINT column from:
If your device is not mounted:
# mount /dev/sdxY /some/directory
And to unmount it, you can use umount on the directory you mounted the disk on:
# umount /some/directory
Now you can create new file systems through console tools or graphic interface tools.
To create a file system you just have to use mkfs which is just a unified front-end for the different
mkfs.fstype tools. E.g.:
# mkfs -t ext4 /dev/partition
To create a swap file system, use mkswap:
# mkswap /dev/partition
There are several GUI tools for partition management:
- Gparted — GTK+ Partition Magic clone, frontend to GNU Parted.
- gnome-disk-utility — Disk management utility for GNOME.
- KDE Partition Manager — KDE utility that allows you to manage disks, partitions, and file systems.