mike <[EMAIL PROTECTED]> wrote:
> On 9/5/07, Joerg Schilling <[EMAIL PROTECTED]> wrote:
> > As I wrote before, my wofs (designed and implemented 1989-1990 for SunOS
> > 4.0,
> > published May 23th 1991) is copy on write based, does not need fsck and
> > always
> > offers a stable view on the media because it is COW.
>
> Side question:
>
> If COW is such an old concept, why haven't there been many filesystems
> that have become popular that use it? ZFS, BTRFS (I think) and maybe
> WAFL? At least that I know of. It seems like an excellent guarantee of
> disk commitment, yet we're all still fussing with journalled
> filesystems, filesystems that fragment, buffer lags (or whatever you
> might call it) etc.
Maybe people did not see that wofs uses two different concepts to allow it to
be optimal for WORM media.
The best documented one is the inverted meta data tree that allows wofs to write
only one new generation node for one modified file while ZFS needs to also
write new
nodes for all directories above the file including the root directory in the fs.
The other one is the fact that COW is the only way to implement a FS on a WORM
media.
COW allows wofs to live without fsck and always grants a conststent fs view on
the
medium.
The inverted tree allows to write few data for modified files and to auto move
the orphaned files to /lost+found during the mount process in the kenel.
Jörg
--
EMail:[EMAIL PROTECTED] (home) Jörg Schilling D-13353 Berlin
[EMAIL PROTECTED] (uni)
[EMAIL PROTECTED] (work) Blog: http://schily.blogspot.com/
URL: http://cdrecord.berlios.de/old/private/ ftp://ftp.berlios.de/pub/schily
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