Increasing the capacity of a replicated file system

You can increase the capacity of a replicated file system by adding disks to the redundancy groups.

Before you begin

  • To perform this task, you must be a Db2® cluster services administrator.

About this task

This task explains how to increase the capacity of a replicated file system by adding disks to the redundancy groups. To ensure high availability at the file system level, it is important to maintain the same capacity in redundancy group 1 and 2 for each file system. When one group has a larger capacity than the other and the group with the smaller capacity becomes full, the file system continues to operate with new data stored in the redundancy group with larger size only, effectively making that file system not highly available. As a result, the best practice is to add the same total size to redundancy groups 1 and 2 at the same time by using the same command. An alert is raised any time the size between redundancy groups 1 and 2 is different. The alert is cleared automatically when the condition is met again.
Figure 1. Multi-site IBM Spectrum Scale replication topology
Multi-site IBM Spectrum Scale replication topology

Procedure

Add two new disks to redundancy group 1 and 2 for db2datafs file system in figure 1.
 db2cluster -cfs -add -filesystem db2datafs -disk /dev/hdisk10,/dev/hdisk11 -rdncy_grp_id 1 -disk /dev/hdisk12,/dev/hdisk13 -rdncy_grp_id 2              
Note:
  • Assuming the above commands result in redundancy groups 1 and 2 having the same total size, no alert is raised.
  • If the file system db2datafs does not have the file system tiebreaker group, an alert is raised about missing redundancy group. Adding the file system tiebreaker group removes the alert automatically.
  • If redundancy group 2 does not exist before issuing the above command and there exists data already in the file system, those data are not replicated automatically at the completion of the above command. Use the replicate command at off-peak usage period to replicate existing data across the two redundancy groups.
  • The capacity of the file system tiebreaker redundancy group need not be increased regardless of the size in redundancy group 1 and 2 because no user data or metadata exists on that disk.