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Technical white paper | HP Enterprise Virtual Array Storage and VMware vSphere 4.x and 5.x configuration best practices
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Figure 23 below illustrate an HP EVA Storage configuration where controller 1 owns Vdisks 1 and 2 and controller 2 owns
Vdisks 3 and 4.
Figure 23. VAAI command pathing and optimal path access
In this configuration, access to the Vdisks by VAAI WRITE SAME and XCOPY commands is summarized in the table below:
Table 9. VAAI command controller access
Command
Operation
Controller Receiving Command
WRITE SAME
Zero addresses on Vdisk1 or Vdisk2
Controller 1
WRITE SAME
Zero addresses on Vdisk3 or Vdisk4
Controller 2
XCOPY
Copy data from Vdisk1 to Vdisk1
Controller 1
XCOPY
Copy data from Vdisk1 to Vdisk2
Controller 1
XCOPY
Copy data from Vdisk1 to Vdisk3 or Vdisk4
Controller 2
XCOPY
Copy data from Vdisk3 to Vdisk3
Controller 2
XCOPY
Copy data from Vdisk3 to Vdisk4
Controller 2
XCOPY
Copy data from Vdisk3 to Vdisk1 or Vdisk2
Controller 1
From the summary in Table 9, we can see that WRITE SAME operations are sent to the optimal “owning” controller for a
Vdisk. So when zeroing multiple Vdisks concurrently, there is a significant performance advantage of zeroing Vdisks owned
by different controllers concurrently over Vdisks that are owned by the same controller.
Similarly, during XCOPY operations, EVA controllers work together to transfer the data from the source Vdisk to the
destination Vdisk using the controller proxy link when the source and destination Vdisks are on different controllers. Hence
for improved performance it is best to perform XCOPY operations between Vdisks that are owned by different controllers.