System information
Procedure
1 In the vSphere Client, select the host in the inventory panel.
2 Click the Configuration tab and click Advanced Settings under Software.
3 Click Disk in the left panel and scroll down to Disk.SchedNumReqOutstanding.
4 Change the parameter value to the number of your choice and click OK.
This change can impact disk bandwidth scheduling, but experiments have shown improvements for disk-
intensive workloads.
What to do next
If you adjust this value in the VMkernel, you might also want to adjust the queue depth in your storage adapter.
Reducing SCSI Reservations
Operations that require getting a file lock or a metadata lock in VMFS result in short-lived SCSI reservations.
SCSI reservations lock an entire LUN. Excessive SCSI reservations by a server can cause performance
degradation on other servers accessing the same VMFS.
Examples of operations that require getting file locks or metadata locks include:
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Virtual machine power on.
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VMotion.
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Virtual machines running with virtual disk snapshots.
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File operations that require opening files or doing metadata updates.
Performance degradation can occur if such operations occur frequently on multiple servers accessing the same
VMFS. For instance, VMware recommends that you do not run many virtual machines from multiple servers
that are using virtual disk snapshots on the same VMFS. Limit the number of VMFS file operations when many
virtual machines run on the VMFS.
Adjust Queue Depth for a QLogic HBA
If you are not satisfied with the performance of your QLogic adapter, you can change its maximum queue
depth.
You can adjust the maximum queue depth for a QLogic qla2xxx series adapter by using the vSphere CLI.
Procedure
1 Verify which QLogic HBA module is currently loaded by entering the following command:
vmkload_mod -l | grep qla2xxx.
2 Run the following commands.
The example shows the qla2300_707 module. Use the appropriate module based on the outcome of the
previous step.
vicfg-module -s ql2xmaxqdepth=64 qla2300_707
In this case, the HBA represented by ql2x will have its LUN queue depth set to 64.
3 Reboot your host.
Fibre Channel SAN Configuration Guide
70 VMware, Inc.