The SCSI Reserve command and the SCSI Persistent Reserve command are specified by the SCSI standards. Servers can use these commands to prevent ports in other servers from accessing the LUN.
This prevents accidental data corruption that is caused when a server overwrites data on another server. The Reserve and Persistent Reserve commands are often used by clustering software to control access to SAN Volume Controller virtual disks (VDisks).
If a server is not shut down or removed from the server cluster in a controlled way, the server reserves and persistent reserves are maintained. This prevents other servers from accessing data that is no longer in use by the server that holds the reservation. In this situation, you might want to release the reservation and allow a new server to access the VDisk.
When possible, you should have the server that holds the reservation explicitly release the reservation to ensure that the server cache is flushed and the server software is aware that access to the VDisk has been lost. In circumstances where this is not possible, you can use operating system specific tools to remove reservations. Consult the operating system documentation for details.
When you use the svctask rmvdiskhostmap CLI command or the SAN Volume Controller Console to remove VDisk-to-host mappings, SAN Volume Controller nodes with a software level of 4.1.0 or later can remove the server reservations and persistent reservations that the host has on the VDisk.