Edmund A. Hajim  School of Engineering and Applied Sciences

Disk Quotas

We have long resisted implementing machine-enforced disk quotas. We have relied on HSEAS users acting in good faith as members of a community. This has allowed users that need large amounts of space to have it available for short periods of time, with the understanding they need to free up space when others need it. Unfortunately, this freedom is rather widely abused, and in many cases 80-90% of the materials on disk have not even been looked at in several months (several years in some cases). Thus we have been forced to use machine-set disk quotas.

While we can implement quotas for disk space and number of files, the number of files a user has does not yet seem to be a problem, and thus we have restricted our disk quotas to space (disk block) consumption only.

We have recommended in most cases a soft limit of 200Mb, and a hard limit of about 500Mb to 1Gb, depending on the nature of the work done and the amount of space available. The soft and hard limits can be set to other values on a per-user basis as necessary (e.g., someone with a short-term project that needs a large amount of space).

To discourage people from hoarding space, we may also implement a system in which an individual's quota limits be reduced each month by a pre-determined percentage based on the amount of 'inactive' material in their account. This is needed because quota limits tend to 'over-subscribe' the space available (rather like airline overbooking). That allows much higher quotas and is much better for those that need lots of space. This works because many users will never approach the quota limits. If you expect everyone will reach or almost reach their soft limit, then you must assign a hard limit of (total space / number of users) and set the soft limit below that - not an appealing or useful scenario.

Some key quota concepts:

What to do when over quota?

You can check your disk space via

du -s {directory}

where '{directory}' is the directory you wish to check (usually your home directory).

You could look for files you haven't accessed in some time.

find {directory} -xdev -type f -atime +{N} -print

where {directory} is the directory of interest and {N} is the age in days of interest, e.g., +180 means list any file not accessed in the last 180 days. For example,

find ~/ -xdev -type f -atime +60 -print

to find all files under your home directory whose access times are 60 or more days ago.

But generally, you know where you are using space, and can locate those files/directories for old projects, accumulated mail, etc. fairly easily.

What we recommend once you identify these directory and file objects:

  1. Simply remove the material you no longer need.
  2. Have some material written to tape; you will need to supply either an appropriate DLT or 8mm tape and arrange to have the systems staff mount the tape for you. We may not have a DLT or 8mm drive in all departments. Contact problem@seas.rochester.edu before you buy a tape.
  3. Write the materials to a CD-R or CD-RW disk. You don't have a CD burner? No problem, we do, and can give you (remote) access to it. All you need do is supply us with a blank CD-R or CD-RW disk. This is very appealing, as the CD can be used in almost any modern (or not-so-modern) system - UNIX, MacOS or Windows.
  4. If the material in question is research-related, and you have research disk space, that material most certainly belongs on that alternate disk, and NOT in your home directory. You may need the OK of the Principle Investigator (PI) to store your research materails on the research disk, and a CNG staff member may need to create a directory for you.
  5. Likewise, if you have one or more research disks, you may want to archive older mail to one of those disks. Some people have archived hundreds of Mb of old mail in their home directory; this is nice to have, but this old mail is rarely used. It causes a great deal of difficulty for others and for backups. We are working on some scripts (programs) that will help you move older mail into an archive off of your home directory. If you are not the PI that bought the disk, then you should store your mail archive on a CD-R unless you have permission from the PI to use his/her disk for your mail archive.
  6. For those items you absolutely, positively must have in your home directory, but which you rarely look at, consider file compression. You can use compress, gzip, or bzip2. Gzip is the most common (and gzip files are understood by WinZip) method. Compress is available on all UNIX hosts, but is much less efficient. Bzip2 is the most efficient compression program we have, but it is not as common as gzip (and I do believe that WinZip cannot uncompress Bzip2'ed files). Note that the compression programs cannot compress files that are already compressed (and jpeg, mpeg, etc. files are already compressed). Also, text and data files compress much better (60-98%) that do binary files (typical compression of about 5-20%)

In some cases, the soft quota may be too small for a particular course. A course that involves CAD work (e.g., using Cadence) or finite element analysis (e.g., PATRAN/NASTRAN), students may need larger quotas. If an instructor finds that the soft quota is too small for a particular course, he or she should send email to problem@seas.rochester.edu requesting a larger quota for the students in that course. The note must include a the course number, list of students (each student's HSEAS login name) in the course, and a reasonable suggestion for the revised soft quota. Quotas will revert to the standard value at the end of the semester. It is best to wait until there is a demonstrated need for a larger quota before requesting one.
Please remember that research materials belong on research disks, and not on home directory disks.

Last modifed: Tuesday, 28-Feb-2012 10:49:16 EST