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From: chowe@bbn.com (Carl Howe)
Newsgroups: comp.unix.large
Subject: Re: Epoch like filesystem
Message-ID: <60058@bbn.BBN.COM>
Date: 15 Oct 90 20:45:50 GMT
References: <QAX%GY^@rpi.edu>
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rodney@sun.ipl.rpi.edu (Rodney Peck II) writes:

>Why not write some code to make a standard sunos system behave like Epoch?

>Basically, this means that the hard disk is paged off to optical disk as
>it fills up.  Then, when the pages that are on the optical disk are
>referenced, they are brought back on line.  The directory information
>stays on the hard disk at all times, making things like "find" run at
>a reasonable speed.

>This could be done the right way (rewrite the kernel with proper paging
>schemes and that sort of thing) or the easy way.

>The easy way would be to do a find of the tree and make things that are
>really old into symbolic links to the new file system on the optical
>disk.  Could be a shell script?

Plan 9 from Bell Labs does a similar sort of thing.  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.

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.  That way
it'd be modular and you could still track OS updates.  Regardless, it
seems like a pretty neat idea.

Carl