LinuxSA Mailing list archives

  From: Matthew Tippett <mtippett@ticons.com.au>
  To  : Mike Earnshaw <mearnshaw@bigpond.com>
  Date: Thu, 2 Sep 1999 08:53:43 +0930 (CST)

Re: Journaling ??

> A couple of months ago I read an article in one of the online Linux
> magazines with regard to journaling (?). A program that tracks changes you
> may make to files etc.
> 
> For the life of me I can not remember what it is. Can anyone oblige?

Althought I haven't really looked to deeply in it, I have discussed some
of the concepts with some people.  Of course I don't know for sure and so
I could be wildly wrong.

A Journaling file system is fast.  The way it works is that instead of
writing to the filesystem all over the disk it does a something akin to
a two phase write.

Firstly, when the system says write the data to disk it goes and writes
the information to a staging area on the disk.  It may know where to
put the data long term, but by writing to the staging area there are
speedups due to all writes occuring in the same area.

In a similar way to cache flushing, according to some policy the information
is moved from the staging area to the actual location on the disk that
it belongs.  This could be seconds or minutes after the original write
occured.

The upshot is that from an application standpoint the data is written
very quickly.  Background processes handle shuffling the data around 
later.

Regards,

matt


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