Technical data

Managing Storage Media
9.11 Managing Disk Space
$ Number of blocks by which a user can exceed the quota.
Each entry in a quota file includes the information shown in Table 9–17.
Table 9–17 Contents of a Quota File
Item Description
General
Identifier or
UIC
Identification code of a user entitled to maintain files on the volume
Usage Number of blocks on the volume taken up by the user’s files
Quota Maximum number of blocks on the volume that the user’s files can take
up before an error message is issued
Overdraft Number of blocks over the quota that the user’s files can take up
The maximum number of blocks permitted to a user on a volume is the sum of
the quota and the overdraft.
A quota file is initialized with an entry for UIC [0,0]. The usage count for this
UIC should not change from 0; in other words, UIC [0,0] should own no files. Its
quota and overdraft, however, serve as defaults in certain situations; set them to
values most likely to be assigned to other UICs as quotas and overdrafts.
How Quotas Are Maintained
During normal use of a volume with a quota file, the system automatically
updates the usage counts as users create, delete, extend, and truncate files.
Users without entries in the quota file are not allowed to create files or allocate
space on the volume unless they have the EXQUOTA privilege.
To create new files, a user must have disk space usage below quota (not
overdraft). If adding a new file or expanding a current file exceeds a user’s
quota, the system prohibits the operation and issues an error message.
A user with an overdraft might be able to extend an open file after exceeding the
disk quota (for example, during an editing session). A user can extend an open
file until usage exceeds the sum of the quota and the overdraft. At this point, the
system prohibits further extensions to the file.
Quota restrictions are not enforced for users with the EXQUOTA privilege;
however, their usage counts are maintained.
How the Rebuild Operation Ensures Quota File Accuracy
When you mount a volume that was not properly dismounted the last time it
was used, the system performs an automatic REBUILD operation. If quotas are
enforced on the volume, this action ensures that the quota file accurately reflects
usage of the disk, under any of the following conditions:
• The system fails
• The volume is physically removed before being dismounted
• A user presses the WRITE PROTECT button
9–64 Managing Storage Media