The restriction of Direct Memory Access (DMA) resources
is one of the known issues and limitations with the
system and an IBM Power SystemsAIX host.
The system 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 support website provides for the most current information
about known restrictions:https://datacentersupport.lenovo.com/
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 that is 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.