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 Explicit ALUA mode (explicit transition) – A host driver can set or change the managing controller

for the Vdisk

EVA arrays also support the following ALUA access types:

 Active-Optimized (AO) – The path to the Vdisk is through the managing controller

 Active-Non-Optimized (ANO) – The path to the Vdisk is through the non-managing controller

ALUA compliance in vSphere 4.x and 5.0

ALUA compliance was one of the major features added to the vSphere 4 SCSI architecture and

remains standard in vSphere 4.1 and 5. The hypervisor can detect whether a storage system is ALUA-

capable; if so, the hypervisor can optimize I/O processing and detect Vdisk failover between

controllers.

vSphere 4.x and 5.0 supports all four ALUA modes:

 Not supported

 Implicit transitions

 Explicit transitions

 Both implicit and explicit transitions

In addition, vSphere 4.x supports all five ALUA access types:

 AO

 ANO

 Standby – The path to the Vdisk is inactive and must be activated before I/Os can be issued

 Unavailable – The path to the Vdisk is unavailable through this controller

 Transitioning – The Vdisk is transitioning between any two of the access types defined above

The following load-balancing I/O path policies are supported by vSphere 4.x and 5.0:

 Round Robin – ALUA-aware

 Most Recently Used (MRU) – ALUA-aware

 Fixed I/O – Not ALUA-aware

Because they are ALUA-aware, Round Robin and MRU I/O path policies first attempt to schedule I/O

requests to a Vdisk through a path that includes the managing controller.

For more information, refer to Configuring multi-pathing.

Vdisk follow-over

Another important concept that must be understood is Vdisk follow-over, which is closely associated

with ALUA.

As described above, ALUA defines which controller in an asymmetric active-active array is the

managing controller for a Vdisk. In addition, follow-over ensures that, when the optimal path to the

Vdisk changes, all hosts accessing the Vdisk change their access paths to the Vdisk accordingly.

Follow-over capability is critical in a vSphere 4.x and 5.0 cluster, ensuring that Vdisk thrashing

between controllers cannot occur. With follow-over, all vSphere servers

accessing a particular Vdisk

update their optimal Vdisk access paths accordingly when the Vdisk is implicitly moved from one

controller to the other.

Backward and forward transitioning

Also known as ESX servers

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HP EVA P6000 Guía de usuario Pagina 5