Journaling filesystem
A journaling file system is a type of file system that keeps journalled metadata to avoid filesystem errors and corruption.
Problems with traditional file systems
In the process of writing data to the hard disk, a file system must write out metadata, which is information about the data on the disk, for example, the location of the data or the names of the files. If, while the file system is writing this metadata, the hard disk is interrupted by, for example, a loss of power, the metadata isn't completely written out and the filesystem may be in an inconsistent state, in which the description of the data doesn't fully match the data itself.
One approach to fixing this problem is to run a program that scans the entire hard disk when the system is restarted, to fix an inconsistencies. Such programs include fsck on Unix and Unix-like systems, scandisk[?] on Microsoft Windows systems, and Disk First Aid[?] on Apple Macintosh systems. Unfortunately this method has two problems. First, rescanning the entire disk is very time consuming. Second, there is the possibility that the scanning program will encounter errors that it cannot fix and that data will be lost.
The answer: Journaling file systems
Journaling file systems approach this problem by writing out a special file called a "journal", which keeps track of the transactions to the disk. If power is suddenly interrupted, the hard disk can reread the journal and fix any inconsistencies that occurred. This is much quicker than a scan of the hard disk, and the journal usually also contains enough information to prevent loss of data.
Journaling file systems are related to Logging file systems[?].
Journaling file systems
Supported by the Linux operating system:
Supported by the Microsoft Windows NT and later operating systems:
- NTFS (Linux also has read-only support for NTFS)
Supported by the Apple Macintosh operating systems:
- HFS+ (Journaling was added to Mac OS X 10.2.2.)
See also:
The result is in form a
stones are not jointed radially, but lie on approximately
"corbelled" arch or vault.
Similar walls to those of Tiryns are found in many places, though
the historical period Viewed these imposing structures with as
those in Argohs) to the Cyclopes, a mythical folk, conceived in
adjective Cyclopian or Cyclopean, whose meaning varies
walls of the Tirynthian type; that is to say, walls built of large
filled with small stones. This style of masonry.html">masonry seems to be always
portions, quite probably of later date, show a very different
wall, though irregular in shape. are fitted together with close
carefully distinguished from Cyclopean, as above defined. Finally,
outside a near approach to what is called ashlar masonry, in which
This is the case near the Lion Gate, the principal entrance to the
of the builder's art in Greece are the "bee-hive" tombs of which
Boeotia, Thessaly, and Crete. At Mycenae alone there are eight
imposing of these, and indeed of the entire class, is the one
Atreus." Fig 26 gives a section through this tomb. A straight
sky, leads to a doorway, B. This doorway, once closed with heavy
which only small fragments now exist and these widely dispersed in
the decoration of this facade rosettes and running spirals played
column which tapered downwards and was ornamented with spirals
unlike the columns of classic times, seems to have been in common
passage, B C, roofed by two huge lintel blocks, the inner one of
which is embedded in the hill, is circular in plan, with a.
On
wordlookup.net
All is still licensed under the GNU FDL.
It uses material from the wikipedia.
|
|