Relay-Version: version B 2.10 5/3/83; site utzoo.UUCP
Path: utzoo!mnetor!seismo!cmcl2!phri!roy
From: roy@phri.UUCP (Roy Smith)
Newsgroups: comp.emacs
Subject: Re: concerning Gnu Emacs backup files
Message-ID: <2550@phri.UUCP>
Date: Mon, 5-Jan-87 13:35:54 EST
Article-I.D.: phri.2550
Posted: Mon Jan  5 13:35:54 1987
Date-Received: Tue, 6-Jan-87 18:46:16 EST
References: <8701050256.AA05804@EDDIE.MIT.EDU>
Reply-To: roy@phri.UUCP (Roy Smith)
Organization: Public Health Research Inst. (NY, NY)
Lines: 45
Keywords: backup files, find
Summary: Backup files waste space (with supporting data)

rms@PREP.AI.MIT.EDU (Richard M. Stallman) writes:
> Backup files are not out of date until months have gone by and it is no
> longer likely you will come across a bug. [...] Making find delete
> everyone's backup files is horrible!  Even if you don't want backup
> files, someone else on the system probably does.  Just delete your own.

	From a purely theoretical standpoint, I agree.  On the other hand,
I'm the guy who buys the disk drives, and I'm the guy people complain to
when we run out of space.  Because of this, I'm also the guy who runs "du"
every few days and chases after disk hogs, and who runs "find" every night
to delete backup files more than 2 weeks old (access time).

	Our 2 Sun file servers happen to have a lot of free space so I
don't delete backup files on them.  I just found (finded?) all the backup
files on those systems and came up with:

    Size   Used         Total Backups       Old Backups (atime > 14 days)

    97 Mb  76%    390 files = 2.8 Mb (2.9%)   338 files = 2.5 Mb (2.6%)
    89 Mb  52%    579 files = 3.9 Mb (4.4%)   425 files = 3.9 Mb (3.7%)

	Actually, I'm surprised that the numbers are that low -- I expected
more like 25% wastage (by which I mean space devoted to backup files; maybe
"wastage" is too biased a word).  What that really says is that most of the
files on disk don't get used very often, something I knew already.  At any
rate, Our Vax typically has its 200 Mbyte user partition 95% full, so the
3-4% I save by trashing old backup files really helps.  I hate to think how
much space is wasted on TOPS-20 systems that save 3-4 versions of every
file (I know, I know, you can make emacs do this on unix as well (and not
save them on TOPS-20), but it's not the default so most people don't).

	For what it's worth, since backup files get deleted only after 2
weeks, they are guaranteed to make it onto a weekly dump tape which gets
kept for at least a month.  Thus, a backup file is really available for
something like 6 weeks.  For longer-term recovery of past versions, we rely
on our daily/weekly/monthly/quarterly tape dump schedule.  Disk space is
still too valuable to waste keeping extra copies of every file around for
eternity.  Maybe when dollar-a-megabyte, Gbyte capacity, fast R/W disks
become available I'll change my mind.
-- 
Roy Smith, {allegra,cmcl2,philabs}!phri!roy
System Administrator, Public Health Research Institute
455 First Avenue, New York, NY 10016

"you can't spell deoxyribonucleic without unix!"