ACP_REBLDSYSD

   ACP_REBLDSYSD specifies whether the system disk should be rebuilt
   if it was improperly dismounted with extent caching, file number
   caching, or disk quota caching enabled. The ACP_REBLDSYSD default
   value (1)  ensures that the system disk is rebuilt. Setting the
   value to 0 means the disk is not rebuilt.

   Depending on the amount of caching enabled on the volume
   before it was dismounted, the rebuild operation may consume a
   considerable amount of time. Setting the value of ACP_REBLDSYSD
   to 0 specifies that the disk should be returned to active service
   immediately. If you set ACP_REBLDSYSD to 0, you can enter the DCL
   command SET VOLUME/REBUILD at any time to rebuild the disk.