Work   and   Cache   Disks   in   Hall A

Robert Michaels, rom@jlab.org, Jefferson Lab Hall A, updated Jan 4, 2008

General info about JLab computers (e.g. what is a work or cache disk ?) can be learned from the computer center. This page pertains to the management of Hall A work and cache disks.

• WORK DISK on JLab CUE

We have several Terabytes of scratch work disk on JLab's Common Unix Environment (CUE). Several partitions are dedicated to "contemporary experiments", while other partitions are for everyone (including contemporary experiments). Contemporary experiments include the one running, the one or two upcoming, and recent experiments. See table below for a list of work disks.

To get to your work area, contemporary or not, follow the link: For the example of e98108, you "cd /work/halla/e98108" on JLab computers. If you are in the Unix group a-e98108 you can write there. You must be in the Unix group corresponding to your experiment. Ask me (rom@jlab.org) to be added to a group or for other questions. Some experiments have multiple disk areas, like /work/halla/e97103/disk1 and /work/halla/e97103/disk2, usually one of these is the "dedicated" disk, the other points to a region on a big "shared" disk.

A "cleanup" script will maintain free space on the work disks. In simple terms, the largest and oldest files are deleted nightly, if necessary, to keep some space free. For the dedicated disks, the spokespersons can elect to have me turn off the cleanup script; but it will run on the shared disks. The cleanup script is described in the appendix below.

IMPORTANT:   Work disks are scratch space and have no backups.   Plan for the possibility that files on /work might be deleted or the disk might die.   Keep important files in /home or in MSS.

• ADAQ WORK DISKS

Thanks to Ole Hansen, we also have several TB of work disk on the adaq Linux cluster (adaql machines, l = linux). Disks are /adaqlN/workM where N = 1,2... and M = 1,2,3...   The running experiment may keep stuff there, e.g. huge root files, etc. But these disks are not backed up. Also, a cleanup script may operate there (see appendix). At the end of the experiment, the adaq work disks are cleaned up (files erased) to make room for the next experiment.

• CACHE DISK

In addition to /work, there are two kinds of /cache disk. One kind is ``hidden'' from users and is used to feed the batch farm from data in MSS. Another kind is open to users and is the temporary repository for MSS data. The latter disks are /cache/halla/EXPERIMENT where EXPERIMENT corresponds to different experiments. See Computer Center Scicomp pages.  

• My response to ``I want more disk.''

Below is the table of CUE work disks assigned to hall A experiments.

Always follow the link (shown in middle column) because this could change to point to another mount point. To find out what Unix group you need to belong to, you can do the following, e.g. for e93049, "ls -la /work/halla | grep e93049", then realizing from this that it is a link to /w/work1601, do this: "ls -la /w/work1601 | grep e93049" and now you can see that you must be in Unix group a-e93049 to write to this disk. Ask me to be assigned to the group.

I remind you that a "dedicated" disk means the physical partition belongs to only that experiment, while a "shared" disk means the link points to an area on a partition which is shared by several other experiments.

List of Hall A CUE Work Disks

The WORK Disk Cleanup Script is similar for CUE disks and ADAQ disks. Every night the disks are checked. If less than 95% full, nothing happens. If greater than 95% full, files will be deleted as follows: Initially, files greater than NB bytes are considered, then NB/(10**i), i=1,2,3...(loop) where NB is big. I.e., first we consider 10 Gbyte files, then 1 Gbyte, then 100 Mbyte, etc. At each level of filesize, files are sorted by last usage; oldest files considered first. A file is deleted only if it has not been used within NDAYS (= 10). After each deletion the disk usage is checked; when it falls below 90% the deletion stops. For dedicated CUE disks, the script can be disabled at request of spokesperson, but it cannot be disabled for any shared disks.