Difference between revisions of "File systems"
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Revision as of 20:00, 19 November 2012
- 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
- 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 (see below) or barriers. Lack of journaling can result in data loss in the event of a power failure or system crash. It may also be inconvenient 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.
- ReiserFS (V3) Hans Reiser's high-performance journaling FS 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. ReiserFS (V3) is not being actively developed at this time. Generally regarded as a good choice for
- 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.Note: The JFS filesystem cannot be shrunk by disk utilities such as gparted.
- XFS is another 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.Note: The XFS filesystem cannot be shrunk by disk utilities such as gparted.
- vfat or 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.
- Btrfs Also known as "Better FS", Btrfs 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.
- 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.
- Swap is the filesystem used for swap partitions.
- NTFS - File system used by windows. Mountable with many utilities (e.g. NTFS-3G).
All the above filesystems with the exception of ext2 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.
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
Step 1: delete old partitions, create new ones
For that you can use
fdisk (for MBR) or
gdisk (for GPT). See partitioning for more information.
# fdisk /dev/<device>
mto display the available commands.
Step 2: create the new file system
To create a file system you just have to use
# mkfs -t ext4 /dev/<partition>
mkfs is just a unified front-end for the different
mkfs.fstype tools, you need to install the packages providing these tools for each filesystem you want to use:
vfat(also known as
There are several GUI tools for partition management: