Recovery groups

IBM Storage Scale RAID divides disks into recovery groups where each is physically connected to two servers: primary and backup. All accesses to any of the disks of a recovery group are made through the active server of the recovery group, either the primary or backup.

Building on the inherent NSD failover capabilities of IBM Storage Scale, when an IBM Storage Scale RAID server stops operating because of a hardware fault, software fault, or normal shutdown, the backup IBM Storage Scale RAID server seamlessly takes over control of the associated disks of its recovery groups.

Typically, a JBOD array is divided into two recovery groups that are controlled by different primary IBM Storage Scale RAID servers. If the primary server of a recovery group fails, control automatically switches over to its backup server. Within a typical JBOD, the primary server for a recovery group is the backup server for the other recovery group.

Figure 1. Minimal configuration of two IBM Storage Scale RAID servers and one storage JBOD. IBM Storage Scale RAID server 1 is the primary controller for the first recovery group and backup for the second recovery group. IBM Storage Scale RAID server 2 is the primary controller for the second recovery group and backup for the first recovery group. As shown, when server 1 fails, control of the first recovery group is taken over by its backup server 2. During the failure of server 1, the load on backup server 2 increases by 100% from one to two recovery groups.