IBM SG24-5131-00 User Manual

Special RS/6000 SP Topics 

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.

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. 

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 

rvsd _ X
rvsd _ Y

rvsd _ X

(lv_ X )

rvsd _Y

(lv_Y )

F a st IP  N e tw o rk