The File System

Managing Your Disk Space


Accounts consume disk space as files are created, copied, edited and mail is sent and received. Disk space is a limited resource and various methods are used to manage it.

On the STOSC cluster, users doing similar work (for example, working on the same project) have their accounts on the same disk. Disk space is used as needed and is managed by the group.

On the STSCIC cluster, each user is assigned a specific amount of disk space or disk quota. Most users have a quota of 30,000 blocks (about 15 megabytes), although the quota may be different depending on your use of the system. (One disk block is 512 bytes.)

Displaying Disk Space

If quotas are used on your cluster, use the SHOW QUOTA command to display information about how much space you have used and how much is available to you. For example:

$ SHOW QUOTA
User [JSMITH] has 16647 blocks used, 13353 available, of 30000 authorized and permitted overdraft of 500 blocks on DISK$USER2

Temporary Disk Space

Three disks provide temporary storage on the Science Cluster (STSCIC)--see Table 3.3. These areas are available to everyone on the cluster on a first come, first serve basis. Files have different life times on different disks; any file not used within a defined period of time is deleted. When a file is edited or modified, the expiration date is reset. That means if you put a file there and use it during the time period, the time-to-live counter, begins again. Note that the cleanup procedure does not run on the weekends, so files that expire on a Saturday or Sunday will not be removed until Monday night.



Table 3.3: Temporary Disks on Science Cluster

The STOSC cluster has one temporary disk storage area, DISK$SCRATCH. The following policies apply to that disk:

For either cluster, you need to create a directory for yourself the first time you use a scratch disk, for example:

$ CREATE/DIR DISK$scratch:[your-username]
You can check to see how much
space is currently available on a disk with the SHOW DEVICE command. Figure 3.3 shows how to see how much space (in 512-byte blocks) is available on DISK$SCRATCH.



Figure 3.3: Displaying Available Disk Space

Removing Multiple Versions of Files: PURGE

Every time a file changes in any way, the VMS file system creates a new file that includes any changes; old versions are retained in their entirety. Consequently, you can quickly fill your directory with several old versions of a file when all you really need to keep is the most recent version. The PURGE command can be used to delete multiple versions of a file. By default, PURGE, deletes all but the highest numbered version of all files in the default directory. Figure 3.4 shows how PURGE is used.



Figure 3.4: Removing Old Versions with PURGE

To remove old versions of only one particular file, type a file name as a parameter, for example:

$ PURGE FILENAME.EXT
File I/O operations use the highest version number of a file whenever you specify a file name without a version number.

Displaying Disk Space
Temporary Disk Space
Table 3.3: - Temporary Disks on Science Cluster
Figure 3.3: - Displaying Available Disk Space
Removing Multiple Versions of Files: PURGE
Figure 3.4: - Removing Old Versions with PURGE

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