Install ext3fs with FAI

[Sebastian Benoit]

Blake Barnett(blake.barnett at developonline.com)@2002.01.18 13:59:24 +0000:
> On Fri, 2002-01-18 at 12:13, chewie at wookimus.net wrote:
> > Are you certain it's faster?  I don't know much about the particulars of how
> > ext3 is implemented, but I was under the impression that a slight performance
> > hit was the tradeoff for journalling. 

It depends on the definition of journalling :) ext3 has 3 different modes,
only in one mode it does full data journaling, so in that mode your data is
safe. In ordered mode, your file meta-data is journaled, your data may not
reach the disk, but you won't have old data in your files (or even data from
different files). And writeback mode means, that your filesystem structure
is guaranteed tom be consitent at any time, so your fsck does not have to
check the disk, just replay the journal up to the first bad transaction.
This means your fsck-time will be very short which is good for todays large
drives. see below for explanation (from mount(8))

> >From listening to Andrew Morton talk about it, he said that much more
> work has been put into ext3 for optimization than for ext2, so for some

Small to medium writes can actually be faster anyway: you just write append
data to the journal, you have no head movement on your disk. Once it's
written to the journal write() returns and to your application it seems
fast. A few seconds later the journal is written out to the actual position
on disk. 

Hope this helps ...
Benno

----- snip -----

 "mount -o data=journal"
        Journals all data and metadata, so data is written twice. This
        is the mode which all prior versions of ext3 used.

 "mount -o data=ordered"
        Only journals metadata changes, but data updates are flushed to
        disk before any transactions commit. Data writes are not atomic
        but this mode still guarantees that after a crash, files will
        never contain stale data blocks from old files.

 "mount -o data=writeback"
        Only journals metadata changes, and data updates are entirely
        left to the normal "sync" process. After a crash, files will
        may contain stale data blocks from old files: this mode is
        exactly equivalent to running ext2 with a very fast fsck on reboot.


-- 
Sebastian Benoit <benoit at mathematik.uni-marburg.de>
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