Epoch like filesystem

[Rob McMahon]

In article <60058 at bbn.BBN.COM> chowe at bbn.com (Carl Howe) writes:
>[In Plan 9] They back up the entire contents of their hard disk to optical
>every night as part of the standard file system tree.  For example, all files
>created or changed today would end up in the file system under /1990/1015/...
>Yesterday's files would be under /1990/1014/....  The hard disk on any given
>day only contains the changes since the last optical backup.  You end up with
>both fast access to recently created data and on-line access to all backups.

Surely you want the recently *accessed* data, not just the recently *created*
data on hard disk ?  Otherwise your system's going to be a bit slow.

>Of course, they have a separate file server machine to do all this magic.
>You'd have to modify the file system to make all the copy on write stuff work
>correctly.  However, perhaps you could simply make it a new file system type
>and run it off the file system switch stuff...

This sounds like an ideal application for SunOS 4.1's Translucent FileSystem
(TFS), where you can have a stack of filesystems mounted one over the other,
with the ones below showing through the holes in the ones above.  Just mount
your hard disk on top of your /1990/1015 system on top of your /1990/1014
system...  When you alter a file it is automatically copied to the top level.
I think you'd still have to have some mechanism to copy recently accessed
stuff up to the top level too.  Is anyone doing anything like this ?

Rob
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Rob McMahon, Computing Services, Warwick University, Coventry CV4 7AL, England