IBM Support

PowerHA: LUN Level Switching

Troubleshooting


Problem

This document explains LUN level switching and provides high-level setup information, plus FAQs.

Resolving The Problem

LUN level switching is a new function provided by PowerHA SystemMirror for i which allows for a local high availability solution with IBM System Storage DS8000, Storwize and FlashSystem similar to what used to be available as switched disks for IBM i internal storage.

With LUN level switching, a single-copy (in other words, non-replicated) IASP is managed by a cluster resource group in a device domain.   IASP volumes located in IBM Storage can be switched between different IBM i systems in a cluster.

A typical implementation scenario for LUN level switching is where multi-site replication using MetroMirror or GlobalMirror is used for disaster recovery and protection against possible storage subsystem outages, while additional LUN level switching at the production site is used for local high availability protection.   This eliminates the requirement for a site-switch in case of potential IBM i server outages.
To Configure LUN level switching for DS8000 or SVC based storage, refer to the following respective manuals:
IBM PowerHA SystemMirror for i Using DS8000 Volume 2 of 4 sg248403.pdf
  • - FAQs



    Q: Is there a session that needs to be started (STRASPSSN/STRSVCSSN) in order for switchable LUNs to work?
    A: No, switchable LUNs operates with only an individual copy description. A session is used to relate two copies of an IASP together with a replication relationship. With LUN switching, there is only ever one copy of the IASP switched so there is no session needed.

    Q: Can I adapt an existing device CRG to use switchable LUNs?
    A: Yes, you should make sure that the recovery domain description (host identifiers and volume groups) are added for all the CRG recovery domain nodes (even the nodes you will be adding) prior to adding any cluster node to the CRG recovery domain.

    Q: Can I use Geo Mirror, Global Mirror, or Metro Mirror with LUN switching?
    A: Yes, all three (not at the same time in a single CRG). You should start an ASP session as you normally would prior to starting the CRG in Step 7 (assuming you have done all the preconfigure work for that particular replication you are using).

    Q: What about on the mirror site, will LUN switching support multiple nodes on the mirror site with replication?
    A: Yes, even with geographic mirroring, you will be allowed to have multiple nodes on your mirror site and use LUN switching to switch the IASP(s) between them.

    Q: Because LUN switching really just switches volume groups between host connections, do I need to enter the LUN numbers in my copy description if I am only going to use LUN switching (no replication)?
    A: Yes, PowerHA verifies the LUNs against the volume groups when the CRG is started; so they need to be entered.

    Q: Do my IOPs/IOAs need to be in an I/O pool like they did with IOP and tower switching?
    A: No, the involved IOPs and IOAs do not need to be in an IO pool.

[{"Type":"MASTER","Line of Business":{"code":"LOB68","label":"Power HW"},"Business Unit":{"code":"BU070","label":"IBM Infrastructure"},"Product":{"code":"SWG60","label":"IBM i"},"ARM Category":[{"code":"a8m0z0000000CGgAAM","label":"High Availability"}],"ARM Case Number":"","Platform":[{"code":"PF012","label":"IBM i"}],"Version":"All Versions"}]

Historical Number

565618921

Document Information

Modified date:
03 October 2024

UID

nas8N1012169

Page Feedback