Managing Disk Space

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HP OpenVMS System Manager's Manual, Volume 1:...

Managing Storage Media

Using Command Procedures for Media Setup

Using the Analyze/Disk_Structure Utility to Check and Repair...

Managing Disk Space

Disk space available for files is finite. You share responsibility with your users for making the best use of disk space.

The following sections explain disk quotas and describe some methods you can use to conserve and monitor disk space:

Method Section

Establish disk quotas
Establishing Disk Quotas

Purge files
Purging Files

Set version limits on files
Setting Version Limits on Files

Set file expiration dates
Setting File Expiration Dates

Analyze and repair error conditions
Using the Analyze/Disk_Structure Utility to Check and Repair Disks

Method	Section
Establish disk quotas	Establishing Disk Quotas
Purge files	Purging Files
Set version limits on files	Setting Version Limits on Files
Set file expiration dates	Setting File Expiration Dates
Analyze and repair error conditions	Using the Analyze/Disk_Structure Utility to Check and Repair Disks

Understanding Disk Quotas

A disk quota is a method for maintaining and enforcing limits on the amount of disk space available to users on a public volume. You limit the amount of space available to individual users on public volumes (or volume sets) by creating and maintaining a quota file on each volume. Individual users can similarly restrict usage on private volumes.

Quotas are maintained and enforced on a per-volume basis. Each volume or volume set has its own quota file. A volume on which quotas are not maintained has no quota file. On a volume set, volume 1 contains the quota file.

With OPER privilege, you (or the user maintaining the volume) supply identifiers and assign quotas and overdrafts with the System Management utility (SYSMAN). (During normal file activities, the system automatically maintains usage counts.)

If users run out of disk space during the creation of a file, they receive a system message. If they cannot obtain sufficient space by purging or deleting unnecessary files, they might contact you to increase their disk quota. If they attempt to write a file to a spooled printer, they must have write access and have sufficient quota on the disk associated with that printer.

Disk Quota File

A quota file records all users who are allowed to use the disk, and shows their current disk usage and their maximum disk allocation. A quota file, QUOTA.SYS, which is stored in directory [000000] with other system files, requires one block of disk storage for every 16 entries.

A quota file has the following format:

  UIC [1]        Usage [2]      Permanent Quota [3]  Overdraft Limit [4] 
[0,0]             0               333333              3333
[TTD,DAVIS]       15590           333333              3333
[TTD,MORGAN]      1929            333333              3333
[MKT,MORSE]       7650            333333              3333
.
.
.

User identification code (UIC) of each user entitled to maintain files on the volume. UIC [0,0] appears in all quota files; use it as a template to set default values for quotas and overdrafts.

Number of disk blocks currently dedicated to a user's files. This number includes the blocks allocated (shown by the DCL command DIRECTORY /SIZE=ALL /BY_OWNER=uic ), plus at least one block in the index file for every file owned by the user.

Maximum number of blocks on the volume that a user's files can occupy. When the maximum number is exceeded, the system issues an error message when a file is created.

Number of blocks by which a user can exceed the quota.

Each entry in a quota file includes the information shown in Contents of a Quota File.

Table 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

**Table 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

Establishing Disk Quotas

Disk quota operations are enabled by default. However, you can use SYSMAN DISKQUOTA commands to control disk usage. You can assign disk quotas to users and maintain an accurate record of disk use for ODS Level 2 or 5 disks. You create a quota file for each disk except the system disk. The quota file records the current usage and the maximum disk usage for all users.

SYSMAN allows you to access disks that are normally unavailable from your local node. With SYSMAN, you can obtain a display of all disks on the other nodes, including those that are mounted privately or used as system disks. You can run DISKQUOTA on any available disk without logging in to each node.

Creating a Quota File

The first step in allocating disk space is to create a quota file for each volume or each volume set. The absolute maximum number of blocks permitted a user on a volume is the sum of the quota and the overdraft. Only users with the EXQUOTA privilege can bypass disk quota restrictions.

How to Perform This Task

Creating a quota file requires SYSPRV, BYPASS, or GRPPRV privilege. To create a quota file on a disk using SYSMAN commands:

Use the DISKQUOTA CREATE command and specify the target disk with the /DEVICE qualifier using the following format:DISKQUOTA CREATE/DEVICE=device-spec
To use the DISKQUOTA ENABLE command on a disk that has been mounted on multiple nodes in a cluster, you must first specify the nodes in the SET ENVIRONMENT command.

Use the DISKQUOTA MODIFY command to adjust [0,0] to an appropriate value for the device using the following format:DISKQUOTA MODIFY/DEVICE=device-spec/PERMQUOTA=value
If you create a quota file or enable disk quotas on a disk that has files on it, use the DISKQUOTA REBUILD command to update the disk quota entries with the current usage information.

Use the DISKQUOTA SHOW command to display the quota file using the following format:DISKQUOTA SHOW owner/DEVICE=device-spec

Examples

```
$ MCR SYSMAN
SYSMAN> SET ENVIRONMENT/CLUSTER
SYSMAN> DISKQUOTA CREATE/DEVICE=DUA12:
```
The first SYSMAN command in this example sets the environment for all nodes in the cluster. The second SYSMAN command sets up the quota file, QUOTA.SYS, in directory [000000] on the DUA12: device.

The quota file has one entry, UIC [0,0], that stores default values for quotas and overdrafts.

```
SYSMAN> DISKQUOTA MODIFY/DEVICE=DUA12: [0,0]/PERMQUOTA=3000
```
The command in this example edits the entry for UIC [0,0] in the quota file on the DUA12: device, setting the default permanent quota to 3000 blocks.

```
SYSMAN> DISKQUOTA SHOW [0,0]/DEVICE=DUA12:
```
The command in this example shows quotas, overdrafts, and usage counts for UIC [0,0] on the DUA12: device.

Monitoring Disk Quotas

Use the commands shown in the following table to monitor the amount of disk space users consume:

Command Description

MOUNT/QUOTA
Use to enforce quotas on a specified disk volume. You must have the VOLPRO user privilege, or your UIC must match the UIC written on the volume.

SHOW QUOTA
Use to determine whether a quota exists for any specific user on a specific disk. The display that results from the SHOW QUOTA command gives the quotas used, authorized, and available.

Enter the DCL command SHOW QUOTA using the following format: SHOW QUOTA/USER=uic (or identifier)

The results of the SHOW QUOTA command depend on whether you have read access to the quota file:
If you have read access, the command shows how much disk space any user on the system has been allocated.

If you do not have read access, the command shows your own allotment.

Command	Description
MOUNT/QUOTA	Use to enforce quotas on a specified disk volume. You must have the VOLPRO user privilege, or your UIC must match the UIC written on the volume.
SHOW QUOTA	Use to determine whether a quota exists for any specific user on a specific disk. The display that results from the SHOW QUOTA command gives the quotas used, authorized, and available. Enter the DCL command SHOW QUOTA using the following format: SHOW QUOTA/USER=uic (or identifier) The results of the SHOW QUOTA command depend on whether you have read access to the quota file: If you have read access, the command shows how much disk space any user on the system has been allocated. If you do not have read access, the command shows your own allotment.

Examples

```
$ SHOW QUOTA
User [DOCUMENTATION,MALCOLM] has 2780 blocks used, 7220 available,
of 10000 authorized and permitted overdraft of 500 blocks on DISK$
```
The SHOW QUOTA command displays the amount of disk space authorized, used, and still available on the current default disk for the present user. The permitted overdraft in this example is 500 blocks.

```
$ SHOW QUOTA/USER=[DOCUMENTATION,JONES]/DISK=XXX1:
%SYSTEM-F-NODISKQUOTA, no disk quota entry for this UIC
```
This SHOW QUOTA command shows that the user with UIC [DOCUMENTATION,JONES] has no disk quota allocation on the XXX1: device.

$ SHOW QUOTA/USER=[DOCUMENTATION,ELAINE]
User [DOCUMENTATION,ELAINE] has 27305 blocks used, 2305 OVERDRAWN,
of 25000 authorized and permitted overdraft of 4000 blocks on DISK$

This SHOW QUOTA command indicates that a user has an overdrawn quota.

Suspending Quota Operations

The SYSMAN command DISKQUOTA DISABLE (which requires SYSPRV privilege, a system UIC, or ownership of the volume), suspends quota operations on a volume in the current management environment; the DISKQUOTA ENABLE command lifts the suspension. You can also suspend quota operations on a volume at mount time by specifying the /NOQUOTA qualifier with the DCL command MOUNT. Disabling quotas requires privileges.

Whenever quotas are enabled on a volume--either implicitly with the MOUNT command or explicitly with the DISKQUOTA ENABLE command--you must update disk quota information using the command DISKQUOTA REBUILD. In updating the quota file, the system adds new UICs and corrects usage counts for each user. (Refer to the HP OpenVMS System Management Utilities Reference Manual for more information.)

How to Perform This Task

To discontinue quota operations on a volume:

Use the following format to execute the DISKQUOTA DISABLE command on each member of the cluster that is mounting the volume:SYSMAN> DISKQUOTA DISABLE

Exit from SYSMAN.

Delete the QUOTA.SYS file in the top-level directory disk: [000000].

Note that the system does not suspend quotas across disk mounts if the QUOTA.SYS file is still present.

Purging Files

One of the best ways to conserve disk space is to purge the following items:

Old versions of files

Before purging files, make sure that the most recent versions are the ones you want to preserve.

System log files that the system generates automatically, such as the operator log and accounting log files

Log files created by the PRINT and SUBMIT commands

Encourage individual users to purge files in their own areas and directories. If necessary, you can purge files from some or all directories. The following examples show purge commands.

Examples

```
$ PURGE/LOG $DISK1:[JONES...]
```
The command in this example purges all files in the directory [JONES] and all the subdirectories below [JONES] on the $DISK1: device. It logs the files that are deleted (displaying their names on the terminal as they are deleted).

```
$ PURGE/KEEP=3 $DISK1:[*...]
```
This example uses wildcard characters to perform global purges and uses the /KEEP qualifier to retain only three versions of each file.

Setting Version Limits on Files

Another way to conserve disk space is to limit the number of file versions that users can create in a directory by using the /VERSION_LIMIT qualifier with the SET DIRECTORY or CREATE DIRECTORY command using the following format:SET DIRECTORY/VERSION_LIMIT=n

Example

$ CREATE/DIRECTORY $DISK1:[JONES]/OWNER_UIC=[200,1]/VERSION_LIMIT=3

In the example, files in account [JONES] cannot exceed three versions. If a user in this directory attempts to exceed the three-version limit, the system purges the file, leaving only the three most recent versions.

Be careful about setting a version limit on the master file directory (MFD). Because the system uses the version limit that you set on the MFD on any directory you create beneath the MFD, users might inadvertently lose important data.

Setting File Expiration Dates

Files-11 uses the expiration date of each file to track the use of the file. The expiration dates aid the disposal of seldom-used files when you use the DCL command BACKUP/DELETE.

File expiration is a file system feature that is available only on Files-11 Structure Level 2 disks.

After you set an expiration date on a volume, the retention periods operate as follows:

When a user creates a file, the expiration date of the file is the current time plus the maximum time set on the volume.

Every time a user accesses a file (for either a read or write operation), the current time is added to the minimum time. If the total is greater than the expiration date, the new expiration date is used. (The new expiration date is calculated from the maximum retention period.)

The expiration date of a frequently accessed file fluctuates between the minimum and maximum period plus the current date. When you set a suitable interval between minimum and maximum retention periods, you can balance between accuracy and efficiency in maintaining expiration dates. Be careful about setting expiration dates; either be very specific, or set the expiration date in the simplest way.

Certain commands and utilities, such as the DIRECTORY command and the Backup utility, can selectively operate on files that are expired. For example, you can enter a command like the following:

$ BACKUP/DELETE PUBLIC:[*...]/BEFORE=TODAY/EXPIRED  MUA0:ARCH20JUN

In this example, the BACKUP command copies to tape and then deletes all expired files. Users might not be aware of file expiration dates, so retain the tape for a substantial period of time.

For more information about the Backup utility, see Backing Up Files and Directories to a Save Set.

How to Perform This Task

To enable the setting of expiration dates, enter the DCL command SET VOLUME in the following format:SET VOLUME device-name[:][,...]/RETENTION=(min,max)

where min and max specify the minimum and maximum retention periods for files on the volume, expressed as delta time values.

If you specify only a single value in the SET VOLUME/RETENTION command, the system uses the value of the minimum retention period; then the maximum retention period is set to twice the minimum or the minimum plus 7 days, whichever is less. For example, you might set the retention period as follows:

$ SET VOLUME PAYVOL1:/RETENTION=(3)

The system uses 3 as the minimum retention period. Twice the minimum is 6 days; the minimum plus 7 is 10. Because the system uses the smaller of the two numbers, the retention period is set to 6.

You can simulate the maintenance of "access dates," which are available in some other operating systems, by setting the retention periods to very small values (for example, 1 hour). Note, however, that doing so substantially increases overhead in the file system.

This feature does not automatically remove unused files; instead, it maintains expiration dates to permit you to develop your own policy for handling files with little or no activity.

If you start maintaining expiration dates on a previously existing volume, be aware that the expiration dates on existing files are 0 until the files are accessed. Files with expiration dates of 0 are considered expired.

Refer to the HP OpenVMS DCL Dictionary for details on the parameters and qualifiers of the SET VOLUME command.

Example

$ SET VOLUME DUA0:/RETENTION=(15-0:0,20-0:0)

In this example, the command sets the minimum retention period to 15 days and the maximum to 20 days.

Using Command Procedures for Media Setup

Using the Analyze/Disk_Structure Utility to Check and Repair...