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From: renglish@hplabsz.HPL.HP.COM (Bob English)
Newsgroups: comp.unix.large
Subject: Re: Epoch like filesystem
Message-ID: <6063@hplabsz.HPL.HP.COM>
Date: 15 Oct 90 21:02:19 GMT
References: <QAX%GY^@rpi.edu>
Reply-To: renglish@hplabsz.UUCP (Bob English)
Organization: Hewlett-Packard Laboratories
Lines: 48

In article <QAX%GY^@rpi.edu> rodney@sun.ipl.rpi.edu (Rodney Peck II) writes:

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

I see two potential problems with this system.  One is minor, the other
potentially troublesome.

Having kernel support for this type of thing gives you reasonably
complete integration into your file system and quick response to
changes.  By the first, I mean that the file is actually a file, stored
in the file system, backed up by the standard tools, and easily
deletable.  Assuming that you have people there who can fill up your
jukebox, then you're eventually going to have to expunge or archive the
stale data from the jukebox, as well.  When that happens, you're going
to have to do something to keep the name/data associations, and you may
wan tot delete the dangling links.  Probably not a killer, but something
to think about.

A bigger problem will be what to do with a file starts getting used
again after being pushed to the jukebox.  As soon as this starts to
happen, you're going to want the data back on the disk, and the symbolic
link approach isn't going to give you that.  If the access rate into the
jukebox isn't too high, you might be able to write a nightly script to
pull files back to the disk, but you'll never know when your jukebox is
about to thrash.

Another minor problem is that this system will appear transparent to the
user, but won't actually be.  Since it won't be able to free up disk
space on demand, the files on the jukebox may not be able to migrate
back without a lot of effort.  What do you do if a large file gets moved
to the jukebox while someone's on vacation and the disk fills up so that
he or she can't move it back?

I don't mean to discourage you from doing this.  It sounds like fun, and
it sounds useful, but you may run into some headaches down the road.
Using the same shell script to ask people to archive voluntarily might
give you most of what you're looking for without causing the same
problems.

>anxiously awaiting the intelligent unix answers....

Me, too.

--bob--
renglish@hplabs