Managing shared memory communications direct

You can enable or disable and set buffer size on an IBM Storage Scale cluster.

Enabling SMC-D on a cluster

By default SMC-D is disabled on IBM Storage Scale. To enable SMC-D on a cluster, complete the following steps:

Set the tscSmcD parameter to yes.
```
# mmchconfig tscSmcD=yes
```
Stop the GPFS daemons.
```
# mmshutdown -a
```
Start the GPFS daemons.
```
# mmstartup -a
```
Check the SMC-D status.
```
# mmlsconfig tscSmcD
```
The sample output is as follows:
```
tscSmcD yes  
```
SMC-D is enabled.

Disabling SMC-D on a cluster

To disable SMC-D on a cluster, complete the following steps:

Set the tscSmcD parameter to no.
```
# mmchconfig tscSmcD=no
```
Stop the GPFS daemons.
```
# mmshutdown -a
```
Start the GPFS daemons.
```
# mmstartup -a
```
Check the SMC-D status.
```
# mmlsconfig tscSmcD
```
The sample output is as follows:
```
tscSmcD no  
```
SMC-D is disabled.

Tuning SMC-D buffer sizes

In IBM Storage Scale, 512K is the default value for SMC-D Send and Receive buffer sizes. The default value of 512K for SMC-D Send and Receive buffer size is achieved by setting the IBM Storage Scale socketRcvBufferSize or socketSndBufferSize variables to 0 (or by not setting it). This value is sufficient for most scenarios. If required, you can change SMC sockets buffer sizes by using the commands:

mmchconfig socketRcvBufferSize=<receive buffer size in bytes>
mmchconfig socketSndBufferSize=<send buffer size in bytes>