Recovery group server parameters

To enable a GPFS cluster node as a recovery group server, it must have the mmchconfig configuration parameter nsdRAIDTracks set to a nonzero value, and the GPFS daemon must be restarted on the node. The nsdRAIDTracks parameter defines the maximum number of vdisk track descriptors that the server can have in memory at a given time. The volume of actual vdisk data that the server can cache in memory is governed by the size of the GPFS page pool on the server and the value of the nsdRAIDBufferPoolSizePct configuration parameter. The nsdRAIDBufferPoolSizePct parameter defaults to 80% of the page pool on the server. A recovery group server should be configured with a substantial amount of page pool, on the order of tens of gigabytes. A recovery group server becomes an NSD server after NSDs are defined on the vdisks in the recovery group, so the nsdBufSpace parameter also applies. The default for nsdBufSpace is 30% of the page pool, and it can be decreased to its minimum value of 10% because the vdisk data buffer pool is used directly to serve the vdisk NSDs.

The vdisk track descriptors, as governed by nsdRAIDTracks, include such information as the RAID code, track number, and status. The descriptors also contain pointers to vdisk data buffers in the GPFS page pool, as governed by nsdRAIDBufferPoolSizePct. It is these buffers that hold the actual vdisk data and redundancy information.

For more information on how to set the nsdRAIDTracks and nsdRAIDBufferPoolSizePct parameters, see Best-practice recommendations for IBM Storage Scale RAID.

For more information on the nsdRAIDTracks, nsdRAIDBufferPoolSizePct, and nsdBufSpace parameters, see the mmchconfig command in the IBM Storage Scale: Command and Programming Reference.