UNIX Disk Space
|UNIX at SLAC|
|Updated: 20 Apr 2005|
SCS maintains several varieties of permanent and temporary disk storage on the SLAC UNIX systems, each appropriate for different levels of ownership, data access, lifetime, and backup. The purpose of this memo is to aid you in selecting the right kind of storage for your needs.
User home directories are allocated in the AFS file system. Each user's home directory is created in its own AFS volume with its own individual disk space quota. You may request an increase in quota by filling out the AFS Quota Request Form. This form includes current guidelines on volume sizes.
You may also use this form to request an additional volume, indicating where, within your home directory tree, you want the new volume mounted, and let us know your plans for the disk space. Planning information helps us to allocate the right kind of disk space to you, and helps us predict disk space growth (see Real Costs of Disk Space) and sometimes enables us to suggest better ways to satisfy your storage needs. For example, space for a project involving more than one person should usually be allocated as group space rather than personal space; and large data files used by I/O-intensive programs should probably not be stored in AFS at all. As a rule of thumb, we usually do not allocate more than a few gigabytes in total to an individual's AFS home directory; such large requests are nearly always an indication that there is a better way of meeting your storage requirements.
With the exception of certain special-purpose group volumes, all AFS volumes are backed up on a regular basis. AFS automatically maintains an on-line copy of the previous day's version of every volume. Your primary backup volume is always available as .backup in your home directory; you can mount other backup volumes yourself when needed. Older files can only be restored by SCS staff. You can request restoration of an older version of one of your AFS volumes via the AFS Volume Restore Request Form Please include a range of dates from which you want the volume restored. We will restore the volume and mount it at a temporary location so that you can copy whatever files you need.
A special variant of group space is for holding and organizing web pages. This space is always in AFS, and follows structure guidelines developed by the WWW technical committee.AFS Quota Request Form to request an FTP directory. Anonymous FTP at SLAC describes how to read from and write into this space.
Each machine also has a local directory named /usr/tmp. It is similar to /tmp, except that it is cleaned up after seven days.
Some machines may also have a local directory named /usr/work, in which files may be stored for up to 30 days.compute farm as /nfs/farm/work. Files are automatically deleted from this directory after 7 days from their last modification date. This filesystem is not backed up. This is a good place to put large files needed by batch jobs.
However, SCS strongly recommends against storing any non-temporary data on your workstation and specifically does not support the storage of such data on your workstation's system disk. Here are some of the reasons:
If you choose to put non-temporary data on your system disk it will be entirely your own responsibility to back it up before, and restore it after, operating system updates. Moreover, if the need to preserve such data prevents the timely installation of a necessary system update, you may be asked to remove your workstation from the SLAC network until the update can proceed.
If you feel your application requires the use of local storage (e.g., for performance reasons) we recommend that you: buy and install a second hard disk so that the system can be re-installed without overwriting your data; and develop and implement a procedure for backing up your data.
A note about the /scswork Filesystem: Our standard installation guidelines include a 1 GB partition mounted at /scswork, provided there's sufficient room on the system disk. This space, if it exists, is reserved for use by SCS only. If you do not wish to give up this space to SCS, please make other arrangements before your disk is partitioned and the operating system installed.