Dell PowerVault MD3820f - Manual (Page 203)

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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
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 controller module does not own the virtual disk,
it rejects the request.
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 controller 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.
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