General guidelines and recommendations for AFM SW and IW mode fileset

Use the IBM guidelines and the recommendations to configure and maintain AFM Single Writer (SW) and Individual Writer (IW) mode fileset.

The IBM guidelines for the deployment of IBM Storage Scale AFM SW/IW are as follows:

AFM filesets and files recommendation
  • The number of AFM SW/IW mode filesets that can be configured in an IBM Storage Scale cluster is up to 100.
  • The number of files in an IBM Storage Scale AFM SW/IW environment is approximately 100 million files in every fileset.
Gateway nodes recommendation
The number of gateway nodes that can be configured in an IBM Storage Scale cluster depends upon the number of AFM filesets. Keep AFM gateway nodes equal to 1/10th of the number of filesets. That is, for 20 AFM SW/IW filesets in a cache cluster, the proposed number of gateway nodes is '2'. So that, every gateway can be assigned up to 10 filesets. The gateway node must have a dedicated role and no other role must be assigned to the gateway node. Gateway nodes are needed at cache Site only. AFM does not need any Gateway node at the home or target site.
Memory and storage recommendation for a gateway node
Random Access Memory (RAM) on the gateway node needs 128 GB. The /var partition space storage needs to be provisioned for bigger storage (based on the number of filesets handled by gateway node * files in fileset * 255 bytes) space for internal usage during the recovery or resynchronization.
Configuration parameters recommendation for AFM
Tunable Value
Pagepool 8G
afmHardMemThreshold 40G
afmNumFlushThreads 8
afmDIO 2
maxFilestoCache 10000
afmMaxParallelRecoveries 3
To set these preceding parameters, use the mmchconfig command. For example, mmchconfig pagepool=4G. For more information about configuration parameters, see Parameters for performance tuning and optimization.
Network and computing requirement
Plan necessary network bandwidth between cache and home clusters to replicate incoming changes based on a workload. This requirement varies based on the workload. The application is slower on AFM SW/IW filesets because of the message that waiting on the gateway node for the replication. This performance hit varies from 1.2x to 4x based on network and gateway node resources. If the gateway node handles many filesets, more computational power is needed for filtering and dependency checking logic.
Limitations
For more information about the limitations of AFM, see AFM and AFM DR limitations.