Users Guide

1 If possible have more than one LUN for data storage to reduce LUN contention and reservation conicts.

2 High numbers of VMs per LUN can also increase LUN contention. Due to varying workloads it is dicult to identify precise guidelines

for VMs per LUN, but it is good practice not to exceed 64 virtual machines per LUN for proper optimization of your particular solution.

3 The following values are recommended for LUN Queue Depth Throttling:

queuefullsamplesize: 32

queuefullthresholdesize: 8

Consult VMware documentation for more details on these settings and how to modify them.

For more information, see the VMware Knowledgebase article, “Controlling LUN queue depth throttling in VMware ESX/ESXi”

(1008113).

4 Setting the Maximum Outstanding Disk Requests for virtual machines:

Dell recommends the following value for Maximum Outstanding Disk Requests From Competing Worlds:

NoOfOutstandingIOsWithCompetingWorlds: 128

Ensure that you use 128 or the lesser value for maximum outstanding disk requests that supports the latest VMware version available.

Consult the VMware documentation for more details on this setting and how to modify it.

For more information, see the VMware Knowledgebase article, “Setting the Maximum Outstanding Disk Requests for virtual

machines” (1268).

5 DiskReservationThreshold:

• VMware denes this value as the “time window within which recounted reservations on a device are permitted (in msec).” This

setting can be used to increase the fairness of LUN reservations from multiple hosts. This setting can be found in the vSphere

GUI.

Dell recommends the following Disk Reservation Threshold:

DiskReservationThreshold 1

6 To help determine if you are getting reservation conicts and to get an additional logging to diagnose storage contention issues, the

following log settings can be helpful:

ReservationBacktrace: 1

Scsi.LogScsiAborts: 1

Scsi.LogCmdErrors: 1

NOTE

: Some reservation conicts are expected, and not all command errors signify a failure. Consult the VMware

documentation for additional information.

Multipath and clustering support for Linux

Installing multipath in Linux

In Linux, multipathing is supported using the device-mapper multipath module.

The device-mapper module should be installed if not part of the default install: device-mapper-multipath-<version>(RHEL) and device-

mapper-<version>(SLES). This can be installed using any of the update manager tools like yum or yast.

Multipath conguration in SLES

1 Modify the multipath.conf le at /etc/multipath.conf with the parameters as suggested inMultipath les for Linux multipath

conguration. If copying the le from Windows, please use dos2unix multipath.conf le once you have copied it over.

2 To start multipath services and enable them to start at reboot:

chkcong multipathd on

Multipath and clustering setup