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active path for some LUNs; however, this configuration is not persistent across reboots. After a reboot, the

LUNs will be on a single HBA. The advantage of this configuration is it prevents unnecessary trespasses of

LUNs in the case of failure.

The failover time can be adjusted at the HBA, ESX, and virtual machine levels. The Fibre Channel SAN

Configuration Guide and iSCSI SAN Configuration Guide found on www.vmware.com

provide

recommendations for setting the failover time at the HBA and virtual machine level.

VMware ESX Server periodically evaluates the state of each path. The default evaluation period is 300

seconds. This can be changed by modifying the /proc/vmware/config/disk/PathEvalTime

vmkernel config value. This can also be done thru the MUI for ESX 2.x by going to Advanced Setting

and changing the Disk.PathEvalTime parameter. The evaluation period can be set to any value between 30

and 1500 seconds. Note that reducing the PathEvalTime causes path evaluation to run more frequently.

This puts a slightly higher CPU load on the system. Reducing this value (to 90 for example) will help

improve failover time (keeping in mind the preceding caveat).

Table 3 shows the failovermode policies supported for ESX 3.5 and ESX 4.0 with CLARiiON storage

systems.

Table 3. Failovermode policies

ESX

version

ALUA

PowerPath

(Failovermode = 4)

ALUA

Native

(Failovermode =4)

PNR mode

PowerPath

(Failovermode =1)

PNR mode

Native

(Failovermode =1)

ESX 4.0

Yes

(CX arrays running

FLARE 26 or later)

Yes

(Fixed or

Round Robin)

(CX4 arrays running

FLARE 28 version

04.28.000.5.704 or

later)

Yes

(CX arrays running

FLARE 22 or later)

Yes

(Round Robin or

MRU)

(CX arrays running

FLARE 22 or later)

ESX 3.5

No No No MRU

(CX arrays running

FLARE 22 or later)

LUN partitioning

LUNs presented to the ESX server are ultimately presented to the virtual machines. Any storage device

presented to any virtual machine is represented as a virtual disk. To the virtual machine, the virtual disk

appears to be a physical disk. A virtual machine can have multiple virtual disks of different/multiple virtual

disk types located on multiple SCSI controllers. A CLARiiON LUN presented to the ESX server can be

partitioned using one of the three methods:

• Raw disks

• VMFS volumes

• Raw device mapping

EMC CLARiiON Integration with

VMware ESX Server

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