Re: Background fsck

[Dan Melomedman <dan@xxxxxxxxxxx>]

Xin LI wrote:
> Finally, using of journalling requires modification to the metadata format,
> which will lead to some problem when users upgrade their system, so a
> converter might be necessary of DFly finally chooses this approach.

It can be done.

Take a look at EXT3. An EXT2 FS is easily converted to EXT3 with a
utility. It also looks as an EXT2 FS if the kernel doesn't have the
EXT3 support compiled in.

An EXT3 (journaling FS) can be converted back to EXT2 with a simple
fsck. Linux developers did get the migration/backwards compatibility
right.

While both softupdates and journaling guarantee metadata safety, the
journaling FS has a huge advantage: journal replay after a crash takes
seconds, while fsck is still required for softupdates, and takes a long
time to run. softupdates are probably faster than journaling for most
cases though.