The restriction of Direct Memory Access
(DMA) resources is one of the known issues and limitations with
the Lenovo Storage V7000 system and an IBM®System p AIX host.
The Lenovo Storage V7000 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
Lenovo support
website provides for the most current information about known restrictions:
http://support.lenovo.com/us/en/products/servers/lenovo-storage
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.