To suit this situation, VMware introduced an alternate feature for use that have ALUA equipment; but not, this is simply not laid out in the ALUA spec.
Query
ALUA followover merely ensures that if server detects a great TPG AAS alter it don’t end in by itself, it does not you will need to return the alteration in the event they sugar daddy sites canada only has usage of TPGs which can be ANO. Effortlessly, which suppresses the newest servers away from attacking to possess TPG AAS and you may, as an alternative, it follow the TPG AAS of array. Numbers 6.4 and you may six.5 instruct ALUA followover communication having TPG AAS.
Figure six.4 reveals a systematic shop diagram in which the option materials was basically got rid of so you can simplify the fresh new drawing . Here, TPG ID 1 is the AO on Day spa, and one another servers send the newest I/O to that particular TPG. TPG ID 2 is ANO, and that i/O is not delivered to they. Such TPGs is actually set up which have ALUA Direct means.
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 an instrument function set up into the stores array. The fresh new standard setting varies according to supplier and you will model.
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 EVA storage arrays.
Determining Device ALUA Setup
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.