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.
Identifying Unit 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 Inquiry 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.
Determining ALUA Allege Signal
In the Section 5, We shown you the way so you’re able to identify all the latest SATP regulations. I’d to-break new screenshots towards the four quadrants so I can tell you the posts of your efficiency. Right here, You will find tried to skinny it off and record just the traces I must inform you. To accomplish this, We utilized the after the command:
This command lists all SATP rules and then uses grep for the string’s model, satp_alua, and ---. This causes the output to have column headers and separator lines, which are the first two lines in the output. The rest of the output shows only the lines with satp_alua in them. Notice that the -we argument causes grep to ignore the case.
In this output, notice that the EMC CLARiiON CX family is claimed by the VMW_SATP_ALUA_CX plug-in, based on matches on the Model column setting being DGC and the Claim Options setting being tpgs_on the.
On the other hand, both LSI and IBM 2810-XIV are claimed by the VMW_SATP_ALUA plug-in, based on matches on the Vendor column, the Model column, and the value of tpgs_on the in the Claim Options column.
NetApp is also claimed by the VMW_SATP_ALUA plug-in, based on matches on the Vendor column and the value of tpgs_into in the Claim Options column only. In this case, the Model column was not used.
IBM DS8000, which is model 2107-900 (listed in the output without the dash), and IBM SVC (listed here as model 2145) are claimed by the VMW_SATP_ALUA plug-in, based on the Vendor and Model columns only, even though the Claim Options column setting is not tpgs_for the.
The remaining rule allows VMW_SATP_ALUA to claim devices with any Vendor or Model column value, as long as the Claim Options column value is tpgs_on. This means that any array afroromance not listed in the preceding rules that returns a nonzero value for the TPGS field in the inquiry response string gets claimed by VMW_SATP_ALUA. You might think of this as a catch-all ALUA claim rule that claims devices on all ALUA arrays that are not explicitly listed by vendor or model in the SATP claim rules.
