Page 153 - DCAP106_OPERATING_SYSTEM_TOOLS

Operating System Tools

Notes In Linux, it’s the partitions are not required to have one possible file system. As long as it
understands it and the file system supports things like permissions and ownership, you are free
to select any file system. Actually, during most distribution installations, you are asked which
file system to choose. The following is a small list of popular file systems around, each with a
brief explanation on its advantages and disadvantages.

z z The ext2 file system is Linux’ old, yet still used file system. It symbolizes extended 2 file
system and is quite simple. It has been in use almost since the birth of Linux and is quite
resilient against file system fragmentation – although this is true for almost all Linux file
systems. It is however slowly being replaced by journalled file systems.
z z An improvement on the ext2 file system is the ext3 file system. It adds, amongst other
things, the concept of journalling.

z z An improvement on the ext3 file system is the ext4 file system. It adds, amongst other
things, support for very large file systems/files, extents, pre-allocation and delayed
allocation and more. The ext4 file system is backwards compatible with ext3 as long as
you do not use extents. Ext4 is frequently seen as the default file system of choice amongst
administrators and distributions.

z z The reiserfs file system is written from scratch. It also offers journalling, however speed
is its main focus. The file system provides quick access to locations with hundreds of files
inside and keeps the disk footprint for small files small. Even though quite popular a few
years back, the file system has been seeing a lack of support through its popular years and
is not frequently advised by distributions any more.

Did u know? The successor of reiserfs, reiser4, is still quite premature and is, due to the
imprisonment of the main developer Hans Reiser, not being developed that actively any
more.
z z The btrfs file system is considered as a promising file system. It addresses concerns
regarding huge storage backend volumes, multi-device spanning, snapshotting and more.
Although its primary target was enterprise usage, it also offers interesting features to home
users such as online grow/shrink (both on file system as well as underlying storage level),
object-level redundancy, transparent compression and cloning.
A journal of file system keeps track of file write operations. It first performs the write (like
adding new files or changing the content of files) in a journal first. Then, it performs the write
on the file system itself after which it removes the entry from the journal. This set of operations
ensures that, if at any point the file system operation is interrupted (for instance through a power
failure), the file system is able to recover when it is back up and running by either replaying the
journal or removing the incomplete entry: as such, the file system is always at a consistent state.
Generally, it is not possible to switch among file systems (except ext2 <> ext3) but as most file
systems are mature enough you do not need to panic “to chose the correct file system”.
Now, if we take a look at our previous mount output again, observe that there is a part of the
line that says which “type” a mount has. Well, this type is the file system used for that particular
mount.

$ mount
/dev/sda8 on / type ext3 (rw,noatime)
proc on /proc type proc (rw)
sysfs on /sys type sysfs (rw,nosuid,nodev,noexec,relatime)
udev on /dev type tmpfs (rw,nosuid,relatime,size=10240k,mode=755)
devpts on /dev/pts type devpts (rw,nosuid,noexec,relatime,gid=5,mode=620)

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