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From: zwicky@erg.sri.com (Elizabeth Zwicky)
Newsgroups: comp.unix.questions
Subject: Re: Disk quotas and the like: is there a standard?
Keywords: unix disk block quota
Message-ID: <1991Jan8.200917.25263@erg.sri.com>
Date: 8 Jan 91 20:09:17 GMT
References: <321@bria.AIX> <1991Jan8.190723.22542@cubmol.bio.columbia.edu>
Sender: news@erg.sri.com
Organization: SRI International, Menlo Park, CA
Lines: 43

In article <321@bria.AIX>  writes:
>The one thing that UNIX (at least the UNIX's that I've worked with) doesn't
>seem to deal with is disk quotas.  One of the things that I liked about
>VMS was the ability to set quotas, set a sort of "grace" quota above that,
>and be able to give a user the privilege to exceed disk quotas.

>Something comparable under UNIX would be useful, and no doubt there are
>quite a few flavors that do use quotas ... the question being, are
>disk quotas part of the POSIX standard?  What flavors of UNIX out there
>do have a quota scheme?
 
I don't know about POSIX; in general, BSD-derived flavours of UNIX do
have quotas, based on file ownerships. They even work adequately on
non-networked file systems for some sites. Mixing quotas with NFS
gives results that can be charitably described as mixed (that is to
say, I do actually know of one situation in which it does work, and in
all the rest it ranges from broken to incredibly broken). I wouldn't
advise it unless you carefully test what happens when you attempt to
go over your quota on a remote system in every possible combination of
local and remote operating systems; a lot of combinations result in
silent failure of over-quota writes, which is liable to upset people.

The normal UNIX quota system works by looking at ownership of files,
and allows one to set a soft quota (it nags at you if you exceed it)
and a hard quota (you can't exceed it). It allows only positive
non-zero quotas. It requires that quotas be explicitly set
per-user-per-filesystem (that is, you must set a quota for each user
on each filesystem; quotas work only per filesystem), and if they are
not defaults to infinity. In most environments, it's not really
satisfactory. Large sites usually run without quotas, using
locally-developed schemes to monitor and control disk usage. For a
discussion of one such scheme, see my paper "Disk Space Management
Without Quotas" in the proceeding of the third Usenix Large
Installation System Administration workshop.

I would dearly love to see a paper that discussed desirable features
of quota systems, and compared existing quota systems of various kinds
in UNIX to what one would like to have, and suggested what someone
with a large site could do. And if someone else would like to write
such a paper (it would be a great topic for a LISA paper) I'd be happy
to provide what help and encouragement I can. 

	Elizabeth Zwicky (zwicky@erg.sri.com)