This particular aspect is known as ALUA followover

This particular aspect is known as ALUA followover

To accommodate this example, VMware brought yet another function for use that have ALUA products; however, this is simply not discussed from the ALUA spec.


ALUA followover just implies that in the event that machine detects an effective TPG AAS changes so it didn’t end up in by itself, it doesn’t just be sure to revert the alteration even when it only has usage of TPGs which might be ANO. Effectively, this inhibits the fresh new machines off fighting to possess TPG AAS and you will, rather, they proceed with the TPG AAS of your own array. Data six.4 and six.5 teach ALUA followover telecommunications that have TPG AAS.

Figure 6.4 reveals a medical sites diagram the spot where the button materials was indeed got rid of to help you clear up the latest diagram . Here, TPG ID 1 ‘s the AO towards Health spa, and you will each other computers posting the fresh We/O compared to that TPG. TPG ID dos try ANO, and i also/O isn’t delivered to it. These TPGs was set up with ALUA Specific form.

Figure 6.5 shows that Host A lost its path to the AO TPG (based on Figure 6.4). As a result, this host takes advantage of the ALUA Explicit mode on the array and sends a SET_TPGS command to the array so that TPG ID 2 is changed to AO and TPG ID 1 is changed to ANO. Host B recognizes that it did not make this change. But because ALUA followover is enabled, Host B just accepts this change and does not attempt to reverse it. Consequently, the I/O is sent to TPG ID 2 because it is now the AO TPG. (Notice that the array moved the LUN ownership to SPB because this is where the AO TPG is located.)

ALUA followover is actually something setting designed on sites range. The latest default mode varies according to the provider and you will design.

Some storage arrays implement the PREF (preference) bit, which enables an array to specify which SP is the preferred owner of a given LUN. This allows the storage administrator to spread the LUNs over both SPs (for example, even LUNs on one SP and odd LUNs on the other SP). Whenever the need arises to shut down one of the SPs, the LUNs owned by that SP (say SPA) get transferred to the surviving nonpreferred SP (SPB). As a result, the AAS of the port group on SPB is changed to AO. ALUA followover honors this change and sends the next I/O intended for the transferred LUNs to the port group on SPB. When SPA is brought back online, the LUNs it used to own get transferred back to it. This reverses the changes done earlier, and the AAS of the port group on SPA is set to AO for the transferred LUNs. Conversely, the AAS of the port group on SPB, which no longer owns the LUNs, is changed to ANO. Again, ALUA followover honors this change and switches the I/O back to the port group on SPA. This is the default behavior of ALUA-capable HP aisle Hoe te zien wie je leuk vindt zonder te betalen EVA storage arrays.

Identifying Product ALUA Arrangement

ESXi 6 host configuration that enables use of ALUA devices is a PSA component in the form of a SATP (see Chapter 5, “vSphere Pluggable Storage Architecture [PSA]”). PSA claim rules determine which SATP to use, based on array information returned in response to an command. As mentioned earlier, part of the inquiry string is the TPGS field. The claim rules are configured such that if a field’s value is nonzero, the device is claimed by the defined ALUA SATP. In the following sections, I show how to list these claim rules and how to identify ALUA configurations from the device properties.

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