A volume rebuild is an operation performed by the MOUNT utility that reclaims any caching space that was active on the volume when it was improperly dismounted. Volume rebuild is performed by default when the volume is mounted unless /NOREBUILD is specified on the MOUNT command.
For a successful rebuild operation that includes reclaiming all of the available free space, you must mount all of the volume set members.
The rebuild may consume a considerable amount of time, depending on the number of files on the volume and, if quotas are in use, on the number of different file owners.
The following caches may have been in effect on the volume before it was dismounted:
- Preallocated free space (EXTENT cache)
- Preallocated file numbers (FILE_ID cache)
- Disk quota usage caching (QUOTA cache)
If caching was in effect for preallocated free space or file numbers, the rebuild time is directly proportional to the greatest number of files that ever existed on the volume at one time. If disk quota caching was in effect, you can expect additional time that is proportional to the square of the number of entries in the disk quota file.
If none of these items were in effect, the rebuild is not necessary and does not occur. To check whether a rebuild is necessary, SHOW DEVICE/REBUILD can be used.
If you use the /NOREBUILD qualifier, devices can be returned to active use immediately. You can then perform the rebuild later with the DCL command SET VOLUME/REBUILD.