Technical data

Managing Storage Media
9.12 Using the Analyze/Disk_Structure Utility to Check and Repair Disks
9.12.4 Erasing Old Home Blocks
When you initialize a volume, the initialize operation might not erase old home
blocks. These are blocks that were created by previous initialize operations. If
a volume that has old home blocks is damaged, you might not be able to recover
the volume without erasing the blocks.
You can erase old home blocks manually by using the /HOMEBLOCKS qualifier
on the ANALYZE/DISK_STRUCTURE command as follows:
$ ANALYZE/DISK_STRUCTURE/REPAIR/HOMEBLOCKS
Note that this operation can take up to 30 minutes to complete.
9.12.5 Creating a Disk Usage File
You can create a disk usage file by using the /USAGE qualifier. The
identification record in the file header contains a summary of disk and
volume characteristics. Following the identification record is a series of summary
records; one summary record is created for each file on the disk. A summary
record contains the owner, size, and name of the file.
Example
$ ANALYZE/DISK_STRUCTURE/USAGE=[ACCOUNT]USAGE_DDA0.DAT DDA0:
In this example, the /USAGE qualifier creates a disk usage file, USAGE_
DDA0.DAT, and places it in the [ACCOUNT] directory.
9.13 Using Mount Verification for Recovery
Mount verification is a recovery mechanism for disk and tape operations. If a
device goes off line or is write-locked while mount verification is enabled, you can
correct the problem and continue the operation.
Without mount verification, a write lock or offline error causes a volume to be
dismounted immediately. All outstanding I/O to the volume is canceled, and all
open files on the volume are closed. Any data not yet written to the volume is
lost.
9.13.1 Understanding Mount Verification
When the system or a user attempts to access a device after it has gone off line,
mount verification is initiated. Usually a device goes off line as the result of a
hardware or user error. Once a device is off line, the hardware (and for some
disks, the software) marks the disk or tape as ‘‘invalid,’’ and I/O requests for that
device fail.
As long as mount verification is enabled, the following operations occur:
1. The software marks the volume to indicate that it is undergoing mount
verification.
2. The software stalls all I/O operations to the disk or tape until the problem is
corrected.
3. The operator communication manager (OPCOM) issues a message to
operators enabled for DISKS and DEVICES or TAPES and DEVICES.
The message announces the unavailability of the disk or tape in the following
format:
Managing Storage Media 9–73