Dell Emulex Family of Adapters - Manual (Page 1029)

Emulex Drivers Version 10.2 for VMware ESXi User Manual P010087-01A Rev. A
3. Configuration
iSCSI Driver Configuration
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To configure the ESXi Server to load the iSCSI driver with this value after each reboot,
run the following commands and reboot the system:
# esxcfg-module -s "ldto=25" be2iscsi
# /usr/sbin/esxcfg-boot -r
# reboot
The im_policy (Interrupt Moderation policy) parameter configures the Emulex iSCSI
driver to use different settings for Interrupt Moderation. An im_policy value of 1
achieves the highest interrupt rate, whereas the value 4 provides the least interrupt
rate. The default value is 2. An im_policy of 0 turns off the Interrupt Moderation
algorithm in the driver.
The large_io option can be used to modify the maximum transfer size in a single SCSI
command. By default, the Emulex iSCSI driver in ESXi supports up to 128 KB and 32
Scatter Gather entries in a single SCSI command. If applications issue I/O requests that
are larger than 128 KB or need more than 32 Scatter Gather entries, the request will be
split into multiple requests by the driver. By specifying large_io=512; the iSCSI driver
can support up to 512 KB of data and a total of 128 Scatter Gather entries in a single
SCSI command.
Note: By setting the option to 512, the amount of physical memory consumed by the
driver increases. Also, though intermediate values between 64 and 512 will be
accepted, the memory used by the driver will be the same as what will be used
for large_io=512.
To set the large_io parameter in ESXi, type the following commands:
esxcfg-module -s large_io=512 be2iscsi --> to set the parameter
esxcfg-module -g be2iscsi --> to view the parameter value
esxcfg-module -i be2iscsi --> to view the options
Even though the VMware operating system can be tuned to accept larger I/O sizes
from guest operating systems, the guest operating systems will also often need to be
tuned to create those larger I/Os. For example, a Windows Server 2008, 32-bit guest
will by default have a maximum transfer size of 64 KB, even if the VMware kernel is
tuned to allow 512-KB I/O transfers. You must modify the guest registry in order to
achieve the maximum transfer rate set in the VMware kernel.
To do this, use the registry editor to add or modify the following entry to change the
maximum transfer size for the Windows guest:
HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\Symmpi\Paramet
ers\Device\MaximumSGList
The formula used to calculate the proper value for MaximumSGList is:

For a 32-bit Windows guest use the following formula:
MaximumSGList = ((Maximum Transfer Size) / 4) + 1

For a 64-bit Windows guest use the following formula:
MaximumSGList = ((Maximum Transfer Size) / 8) + 1
For example: to allow a 256 KB transfer size on a 32-bit guest, this would be the formula
to use: 256 / 4 = 64 + 1 = 65 (decimal) or 0x41(hexadecimal).