To match this case, VMware brought another function for use with ALUA devices; but not, this is not discussed on the ALUA specification.
Query
ALUA followover merely ensures that if the host finds an effective TPG AAS change this don’t lead to by itself, it will not you will need to return the alteration in the event they has only use of TPGs which might be ANO. Efficiently, which suppresses the hosts away from attacking to own TPG AAS and you will, rather, they follow the TPG AAS of your own array. Numbers six.4 and you may 6.5 instruct ALUA followover communications with TPG AAS.
Figure six.4 shows a clinical shop drawing in which the option textiles was in fact eliminated to make clear the fresh new diagram . Here, TPG ID step one is the AO with the Health spa, and you can one another servers upload the newest We/O compared to that TPG. TPG ID 2 is ANO, and i also/O is not taken to they. Such TPGs is configured which have ALUA Direct 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 was a tool mode set up into the stores range. The latest standard form may differ with regards to the vendor and you may 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. Straight single dating site 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.
Distinguishing Tool ALUA Setting
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.