SCF Reference Manual for the Storage Subsystem (G06.27+, H06.04+)

Managing Magnetic Disks
SCF Reference Manual for the Storage Subsystem—529937-008
7-17
Correcting Doubly Allocated File Extents
Correcting Doubly Allocated File Extents
The REBUILDDFS attribute (page 14-71) of the CONTROL DISK command rebuilds
the disk free space table. This process also gets rid of doubly allocated file extents.
File extent overlaps (doubly allocated file extents) are caused by a hardware or
software error. A doubly allocated file extent is an error condition that occurs when the
same page is allocated more than once to a single file, to two different files, or to a file
and available free space. Report such errors to your service provider. Use the
procedures described next to resolve the problem.
Considerations for the REBUILDDFS attribute
Use this attribute if one of these events occurs:
•
File-system error 58 has occurred (the disk free space table is marked bad).
•
The results from a DSAP command indicate that free space has been lost over
time.
•
You have resolved a problem with doubly allocated file extents (by purging one
of the two conflicting files).
If DSAP reports that a file has doubly allocated file extents, and if the message
“(SQL Shadow)” appears on the same line as the file name, the file is an SQL
table that has been dropped, but the drop is not yet committed. Such a file is
not available to a TACL FILES command or FUP INFO command. The DSAP
DETAIL or SQLCI FILEINFO report can also show the SQL shadow label.
Identifying Doubly Allocated File Extents
To identify any doubly allocated file extents:
-> DSAP $DATA00, FREESPACE
Rebuilding the Disk Free Space Table
1. Stop all applications using the disk.
2. Verify the specified volume is in the STARTED state.
3. Before initiating the REBUILDDFS operation, you must resolve any disk errors,
such as unspared sectors or doubly allocated file extents:
•
Sparing a Defective Sector on page 7-14
•
Correcting Doubly Allocated File Extents on page 7-17
4. To rebuild the disk free space table:
-> CONTROL $DATA00, REBUILDDFS