Brocade Communications Systems StorageWorks 4400 - Enterprise Virtual Array Manual do Utilizador descarregar pdf (Página 20)

Figure 11. Asymmetric datastore group configuration

Optimizing performance

ESX SAN load balancing and HP StorageWorks EVA

The EVA 4x, 6x, and 8x models are active/active arrays and are compliant to the Asymmetric Logical Unit

Access (ALUA) industry standard for LUN failover and I/O processing. Each EVA array includes two

storage controllers and allows I/O through both controllers. However, only one controller is assigned as the

preferred (managing) controller of the LUN. The managing controller can issue I/O commands directly to

the virtual disk. The non-managing controller, better known as the proxy controller, can accept I/O

commands but cannot issue I/O commands to the Vdisk.

If a read I/O request arrives on the non-managing controller, the read request must be transferred to the

managing controller for servicing. The managing controller issues the I/O request, caches the read data,

and mirrors that data to the cache on the non-managing controller, which then transfers the read data to the

host. Because this type of transaction, called a proxy read, requires additional overhead, it potentially

provides less than optimal performance. (There is little impact on a write request because all writes are

mirrored in both controllers’ caches for fault protection.)

When configuring VMware ESX server storage adapters and multipathing, ALUA causes additional design

considerations. By default, VMware Infrastructure 3 only uses one path from the host to a given LUN at any

given time; regardless of path policy. If the path fails, the ESX Server detects and selects another path for

failover. A path is defined as a connection between a host bus adapter port and an EVA controller port.

Using dual ported c-class blade FC HBA with the EVA4400 results in four possible paths

As shown in Figure 12, the default active path uses FC HBA1 (vmhba1) and the EVA controller port with the

lowest PWWN, typically Controller 1 Port 1. The VMware ESX 3.5 multipathing stack does not

automatically balance the load across all of the available data path or privilege direct path to the EVA

virtual disk managing controller.

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