Known AIX issues and limitations

The restriction of Direct Memory Access (DMA) resources is one of the known issues and limitations with the system and an IBM Power Systems AIX host.

The Lenovo Storage V series does not impose a size limitation on volumes for AIX hosts. Check your AIX documentation to determine whether the AIX system itself restricts volume size.

The following Web sites provide for the most current information about known restrictions:

For Lenovo Storage V3700 V2 and Lenovo Storage V3700 V2 XP: https://datacentersupport.lenovo.com/us/en/products/storage/lenovo-storage/v3700v2/6535
For Lenovo Storage V5030: https://datacentersupport.lenovo.com/us/en/products/storage/lenovo-storage/v5030/6536

On a heavily loaded system, the following symptoms can indicate that the host is low on direct memory access (DMA) resources:

You might see errors that indicate that the host bus adapter (HBA) was unable to activate an I/O request on the first attempt.
You might see lower-than-expected performance with no errors being logged.

To reduce the incidence of these messages, you can increase the resources by modifying the maximum transfer size attribute for the adapter as follows:

Type the lsattr -El HBA -a max_xfer_size command to view the current setting, where HBA is the name of the adapter logging the error. For this example, the HBA is fcs0.
Type the chdev -l fcs0 -P -a max_xfer_size=0x1000000 command to increase the size of the setting.
Note: To view the range of allowable values for the attribute, type lsattr -Rl fcs0 -a max_xfer_size.
Restart the host to put these changes into effect.