Converting a non-replicated file system to a replicated file system

You can convert an existing non-replicated file system to a replicated file system.

Before you begin

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

About this task

This procedure is applicable to both single-site pureScale® cluster and a Geographically Dispersed pureScale Cluster (GDPC). With the latter, this is part of the steps in creating a GDPC cluster that involves creating a minimal non-GDPC cluster with non-replicated file system as the primary step. To illustrate the steps that are involved with figure 1 or 2, assume that the cluster has file systems created on storage 1 only. In other words, redundancy group 2 and tiebreaker are not defined. The cluster is operating with a single storage controller.

Figure 1. Multi-site IBM Spectrum Scale replication topology

Procedure

To enable IBM Spectrum Scale replication in the cluster, do the following steps:

Group all disks currently in each file system into redundancy group 1, by using the following commands.
```
db2cluster -cfs -enablereplication -filesystem <fs name>
```
Repeat the command for each non-replicated file system. In figure 1, assume that all three file systems are non-replicated with disks that reside on storage 1 only. To convert the disks to replicated, run the following commands:
```
db2cluster -cfs -enablereplication -filesystem db2sd_1
db2cluster -cfs -enablereplication -filesystem db2datafs
db2cluster -cfs -enablereplication -filesystem db2logfs
```
At the completion of this step, all existing disks in each file system are assigned redundancy group ID 1. Any additional disks added to the file system after this step requires a redundancy group ID specified. Also no user data is replicated yet because secondary storage is not defined.
Add disks to redundancy group 2 and the file system tiebreaker group to complete the disk setup.
```
db2cluster -cfs -add -filesystem <fs name> -disk <disk1,...diskn> -rdncy_grp_id 2 -fstiebreaker <disk> -host <TB hostname>
```
Accordingly, for example, in figure 1, run the following commands to add the disks to each file system :
```
db2cluster -cfs -add -filesystem db2sd_1 -disk /dev/hdisk4 -rdncy_grp_id 2 -fstiebreaker /dev/hdisk7 -host TB
db2cluster -cfs -add -filesystem db2datafs -disk /dev/hdisk5 -rdncy_grp_id 2 -fstiebreaker /dev/hdisk8 -host TB
db2cluster -cfs -add -filesystem db2logfs -disk /dev/hdisk6 -rdncy_grp_id 2 -fstiebreaker /dev/hdisk9 -host TB
```
At the completion of this step, the disk layout of the replicated file systems are completed. New data added to the file system after this step is replicated across redundancy groups 1 and 2 automatically. However, data that existed in the non-replicated file system before conversion is not replicated automatically. The replication and possibly rebalance of existing data needs to be triggered separately and individually. Since these two operations are I/O intensive and the duration depends on the actual size of data, it is recommended to run them at off-peak usage hours. For more information, see Replicating non-replicated data and Rebalancing a replicated file system.