Administrator Guide

Configuring Asymmetric Logical Unit Access

If your MD Series RAID storage array supports Asymmetric Logical Unit Access (ALUA), active-active throughput allows I/O to pass from

a RAID controller module to a virtual disk that is not owned by the RAID controller. Without ALUA, the host multipath driver is required to

send data requests targeted to a specific virtual disk to the owning RAID controller module. If the RAID controller module does not own

the virtual disk, it rejects the request.

Topics:

• ALUA performance considerations

• Automatic transfer of ownership

• Native ALUA support on Microsoft Windows and Linux

• Enabling ALUA on VMware ESXi

• Verifying ALUA on VMware ESXi

• Verifying if host server is using ALUA for MD storage array

• Setting round-robin load balancing policy on ESXi-based storage arrays

ALUA performance considerations

While ALUA enables an MD-series storage array with a dual-controller (duplex) configuration to service I/O requests through either RAID

controller module, performance is decreased when the non-owning RAID controller module accesses a virtual disk. To maintain the best

possible throughput, the host driver communicates with the RAID firmware to send data requests to the owning RAID controller, if

possible.

Automatic transfer of ownership

The RAID controller firmware automatically transfers virtual disk ownership if more than 75 percent of data I/O over the previous five

minutes was routed to the non-owning RAID controller. This indicates that either the storage array has lost redundant connections or that

some of the data paths to the virtual disk or disk group are not usable. MD Storage Manager launches the Recovery Guru (Virtual Disk Not

on Preferred Path) if the condition still exists after the default alert five-minute delay time has expired. For more information, see

Recovery Guru.

Native ALUA support on Microsoft Windows and

Linux

The following operating systems supported by your MD Series storage arrays also support ALUA natively:

• all supported Microsoft Windows operating systems

• Red Hat Enterprise Linux 6.2

• SUSE Linux Enterprise Server 11.2 with Service Pack 2

NOTE: No configuration steps are required to enable ALUA on the operating systems listed above.

Enabling ALUA on VMware ESXi

VMware ESXi 5.x does not have Storage Array Type Plug-in (SATP) claim rules automatically set to support ALUA on the MD Series

storage arrays. To enable ALUA, you must manually add the claim rule.

Manually adding SATP rule in ESXi 5.x

To manually add the SATP rule in ESXi 5.x:

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