IBM SG24-5131-00 manual Recoverable Virtual Shared Disk, D e Z

impact of servicing a local I/O request through VSD relative to the normal VMM/LVM pathway is very small. IBM supports any IP network for VSD, but we recommend the switch for performance.

VSD provides distributed data access, but not a locking mechanism to preserve data integrity. A separate product such as Oracle Parallel Server must provide the global locking mechanism.

9.3.2 Recoverable Virtual Shared Disk

Recoverable Virtual Shared Disk (RVSD) adds availability to VSD. RVSD allows you to twin-tail disks, that is, physically connect the same group of disks to two or more nodes, and provide transparent failover of VSDs among the nodes. RVSD is a separately-priced IBM LPP.

	Fast IP N etwork
V S D S erver	V S D S erver	V S D C lien t
N o d e X	N o d e Y	N o d e Z
	rvsd _ X
	rvsd _ Y
V S D	V S D	V S D
rvsd _ X	rvsd _Y
(lv_ X )	(lv_Y )

Figure 19. RVSD Function

With reference to Figure 19 above, Nodes X, Y, and Z form a group of nodes using VSD. RVSD is installed on Nodes X and Y to protect VSDs rvsd_X and rvsd_Y. Nodes X and Y physically connect to each other’s disk subsystems where the VSDs reside. Node X is the primary server for rvsd_X and the secondary server for rvsd_Y, and vice versa for Node Y. Should Node X fail, RVSD will automatically fail over rvsd_X to Node Y. Node Y will take ownership of the disks, varyon the volume group containing rvsd_X and make the VSD available. Node Y then serves both rvsd_X and rvsd_Y. Any I/O

Special RS/6000 SP Topics 193