3.7.0 HP StorageWorks HP Scalable NAS File Serving Software administration guide - HP Scalable NAS 3.7 for Linux (AG513-96002, October 2009)

Host Bus Adapters (HBAs)
Reduce the HBA queue depth
The HBA queue depth is the maximum number of outstanding I/O requests that the
HBA can hold while it is waiting for responses from the LUNs on the storage array.
If the HBA is sending more I/O requests than the array queue can handle, you may
see I/O performance problems such as the following:
• “Recovered I/O” error events in /var/log/messages
• Sluggish I/O in Await or SVCTM as measured in iostat -x 5
• Reports of “DLM lock stalls” for locks over filesystem I/O
You may be able to eliminate these problems by changing or adapting your workload.
For example, you might move jobs from a heavily loaded node to a less busy node
or reschedule certain activities.
If you are unable to change the workload, try reducing the HBA queue depth, as
described below.
NOTE:
This procedure should be used only if HP Scalable NAS controls the loading of the
HBA driver. If you are using third-party MPIO software such as EMC PowerPath,
HDLM, or IBM RDAC in which the HBA driver load is controlled by the initrd image,
do not use this procedure. Instead, changes to the HBA queue depth should be made
only under the advice and direction of the third-party MPIO vendor.
Determine a value for the HBA queue depth
Consult the hardware vendor for your array to determine the number of supported
SCSI command tags per port/LUN. Then divide that number by the number of servers
in the cluster. For example, if the storage queue depth is 32 and there are eight
servers in the cluster, you would use 4 as the HBA queue depth.
If you are unable to determine the queue depth for the array, try setting the HBA
queue depth to 4.
SAN maintenance376