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How To Use Consistent_Lun setting on VMAX Initiator Groups

Introduction

Using the consistent_lun setting we eliminate the issue where different devices show different lun id’s. This is more prevalent with ESX Hosts. For this to work the flag must be set at creation time of the host and parent initiator groups.  In this post we will cover how to complete the task.

Step 1 – Create Host Initiator Groups

The first step is to create the host initiator groups using the symaccess command

$ symaccess -sid <sid> create -name MYSERVER01_IG -type initiator -consistent_lun -wwn 50060b0000c2abcd
$ symaccess -sid <sid> -name MYSERVER01_IG -type initiator -wwn 50060b0000c2be0e add

Use the -detail flag to see that it is switched.

$ symaccess -sid <sid> show MYSERVER01_IG -type initiator -detail

Symmetrix ID :<symmetrix_sid>
Initiator Group Name : MYSERVER01_IG Last update time : 12:55:44 PM on Thu Sep 24,2015 Group last update time: 12:55:44 PM on Thu Sep 24,2015 Port Flag Overrides : No Consistent Lun : Yes

Step 2 – Create Parent Initiator Groups

Now that we have created the host initiator group and have set the consistent_lun flag we need to create the parent initiator group and set the consistent_lun flag as well. In this example we are creating we are creating a parent initiator group called ESX_PROD_WINDOWS_IG and assigning three host initiators to the group, all of which were created using the consistent_lun flag.

$ symaccess -sid <sid> create -name ESX_PROD_WINDOWS_IG -type initiator -consistent_lun -ig MYSERVER01_IG
$ symaccess -sid <sid> -name ESX_PROD_WINDOWS_IG -type initiator -ig MYSERVER02_IG add
$ symaccess -sid <sid> -name ESX_PROD_WINDOWS_IG -type initiator -ig MYSERVER03_IG add

As with the Host initiator group we can use -detail to validate the group was created correctly.

$ symaccess -sid <sid> show ESX_PROD_WINDOWS_IG -type initiator -detail

Symmetrix ID : <symmetrix_sid>

Initiator Group Name : ESX_PROD_WINDOWS_IG
Last update time : 01:19:40 PM on Thu Sep 24,2015

Group last update time: 01:19:40 PM on Thu Sep 24,2015

Port Flag Overrides : No
Consistent Lun : Yes

Group Name : MYSERVER01_IG
User-generated Name : N/A
FCID Lockdown : N/A
Heterogeneous Host : N/A
Port Flag Overrides : N/A
CHAP Enabled : N/A
Type : Initiator Group

Group Name : MYSERVER02_IG
User-generated Name : N/A
FCID Lockdown : N/A
Heterogeneous Host : N/A
Port Flag Overrides : N/A
CHAP Enabled : N/A
Type : Initiator Group

Group Name : MYSERVER03_IG
User-generated Name : N/A
FCID Lockdown : N/A
Heterogeneous Host : N/A
Port Flag Overrides : N/A
CHAP Enabled : N/A
Type : Initiator Group

Errors

If you try to add a host initiator group that does not have the consistent_lun flag you will be stopped from adding and will get the following error.

$ symaccess -sid <sid> -name ESX_PROD_WINDOWS_IG -type initiator -ig MYSERVER04_IG add

The operation will result in consistent lun violation

Conclusion

As we can see using the consistent_lun flag we can force consistency with lun id’s when storage is shared between many hosts. This is a good practice as it reduces the amount of possible data corruption and access errors hen used.

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