Dell Emulex Family of Adapters - Manual (Page 1030)

Emulex Drivers Version 10.2 for VMware ESXi User Manual P010087-01A Rev. A
3. Configuration
iSCSI Driver Configuration
1030
The maximum value allowed for MaximumSGList is 255 or 0xFF. For the particular
value of 0xFF, the internal value passed to Windows is increased to 0x101, allowing
support for a full 1-MB transfer (2 MB for 64-bit).
The MaximumSGList is 129 for a 512-KB transfer.
Other guest operating systems may also need to be tuned similarly. Consult the tuning
guides that accompany those operating systems.
Interrupt Moderation Policy Settings
Interrupt Moderation Policy settings control the rate of interrupts for the adapter. By
default, the driver implements an Interrupt Moderation scheme that is based on the
I/O load and the interrupt rate. The default setting for the Interrupt Moderation Policy
attempts to vary the interrupt rate between 3500 to 10000 interrupts per second. In
addition, the Emulex iSCSI driver allows other configuration settings which are listed
in the following table.
While the default setting of Moderate may work for most configurations, there are
instances when the setting may need to be altered. Changing the Interrupt Moderation
Policy setting should be based on the initiator system configuration, the number of
iSCSI targets that will be connected, the I/O load, and the throughput and latency
offered by these iSCSI targets.
On systems capable of sustaining a higher interrupt rate and when the number of
targets that will be connected is less (up to 8), the more Aggressive setting will result in
lower latency and higher values of I/O operations per second (IOPs). But the higher
interrupt rate could also result in system stalls and freezes, especially during higher
values of queue depth and smaller sized I/O requests.
On a configuration that involves a large number of iSCSI targets (more than 32 or 64)
and higher values of queue depth, the default setting may prove to be too aggressive
and the Interrupt Moderation setting may need to be changed to Conservative or Very
Conservative. Though this will increase latency of an I/O request, the lower interrupt
rate may allow the system to be functional under a high load.
Table 3-6 Interrupt Moderation Policy Settings
Setting Parameter Description
Disabled im_policy=0 Interrupt Moderation algorithm is turned off in the driver.
Aggressive im_policy=1 Achieves the highest interrupt rate among all available
settings.
Moderate im_policy=2 This is the default value.
Conservative im_policy=3 Achieves a lower interrupt rate than Moderate.
Very Conservative im_policy=4 Achieves the minimum interrupt rate among all available
settings.