In a Shared storage environment, many sets of front end hosts may also visit the same table storage equipment, if the multiple hosts at the same time on a LUN to write operation, then one can imagine the LUN will not know which data to write, write what data. In order to prevent this kind of circumstance happening in data damage, so have the concept of SCSI lock. Through the SCSI Reservation mechanism for SCSI lock operation, at present most of the disk support "SCSI reservvation command". If a host to the disk transfer a SCSI Reservation orders, the disk for other host is in the locked position. If there are other host to have been lock disk send request, speaking, reading and writing, it will receive 'reservation conflict' error information. If keep SCSI lock host collapse, or other host to disk send 'break reservation or reset target orders, used to remove SCSI lock. Then, the second HP G70-213EM cpu fan to send the I/O request before need to send SCSI Reservation command to disk.
SCSI - 2 Reservation only allow device is a SCSI locked Initiator access, also is the host HBA. Such as host 1 to visit the HBA1 LUN add SCSI - 2 lock, at this time even if the host 1 HBA2 cannot visit this LUN. So SCSI - 2 Reservation is also called Single Path Reservation.
SCSI - 3 Reservation (Persistent Reservation) is the use of PR Key to disk to lock. Usually a Host will have only PR Key, different Host corresponding PR Key is also different. So the general SCSI - 3 Reservation is usually used in the sharing of the HP Pavilion dv5-1206ax cpu fan under the environment. Here SCSI - 3 Reservation, also called the Persistent Reservation.
Windows 2003 cluster using SCSI - 2 reserve/release command. As the lasting reservation, so a node in the cluster will hold SCSI - 2 reservation lock, and then every 3 seconds to refresh a. If the fault transfer occurs, the switch node main chance in the corresponding placed on disk SCSI - 2 Reservation then maintenance SCSI lock. If all nodes on the host of the cluster service will be closed, Reservation also won't keep.
Windows 2008 cluster using SCSI - 3 persistent reservation mechanism. If the Disk from the host do not have the right to remove, Cluster use Disk (Cluster Disk) will keep the Reservation. Lock the corresponding SCSI lock will always exist in the corresponding disk on, even if the cluster service is closed or disk for host cancel hide (unmasked). So, sometimes need to forcibly remove disk on the Reservation.
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