To tune the LLT variables for RDMA links

1. Append the /etc/sysconfig/llt file with the following value.

   LLT_MAXADVBUFS=4000

   When you increase the number of receive-buffers to a maximum value of 4000 the IO performance improves, provided the cluster nodes have sufficient memory.

2. If the typical IO size is lesser than the average IO size, you can avoid memory wastage by tuning down the receive buffer size to a minimum of 8K. By default, the receive buffer size is 64K.

   Append the /etc/sysconfig/llt file with the following value.

   LLT_ADVBUF_SIZE=8192

3. Append the /etc/llttab file with the following values.

   set-flow highwater:10000
   set-flow lowwater:8000
   set-flow window:5000
   set-flow rporthighwater:10000
   set-flow rportlowwater:8000
   

4. Restart the SFCFS or SFCFSHA stack for changes to take effect.

To verify the LLT tunable values

• Check the LLT configuration.

  # lltstat -c

  LLT configuration information:
      node: 0
  .
  .
      max advertised buffers: 4000
      advertised buffer size: 8192