Stretched Cluster on IBM SVC (Part 3)

This is part 3 of the VMware Stretched Cluster on IBM SVC blogpost series.

PART 1     (intro, SVC cluster, I/O group, nodes)
PART 2     (split I/O group, deployment, quorum, config node)
PART 3    (HA, PDL, APD)

 

I explained how a SVC Split Cluster reacts to certain failure conditions in part 2. Now that we know how the storage layer behaves, let’s take a closer look at how this all ties in with the VMware layer. This is by no means a complete guide to every setting/configuration option involved, more of an excerpt of the ones I consider to be important. This post is based on vSphere 5.5.

VMware Stretched Cluster isn’t a feature you enable by ticking some boxes, it’s a design built around the workings of HA, DRS and a couple of other mechanisms.

First, I would like to briefly explain the concepts APD (All Paths Downs) and PDL (Permanent Device Loss).

 

APD

In an All Paths Down scenario, the ESXi host loses all paths to the storage device. The host is unable to communicate with the storage array. Examples of failures that can trigger APD are a failing HBA or a failing SAN.

APD All Paths Down

figure 1. APD

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Stretched Cluster on IBM SVC (Part 2)

This is part 2 of the VMware Stretched Cluster on IBM SVC blogpost series.

PART 1     (intro, SVC cluster, I/O group, nodes)
PART 2    (split I/O group, deployment, quorum, config node)
PART 3     (HA, PDL, APD)


SVC split I/O group
It’s time to split our SVC nodes between failure domains (sites). While the SVC technically supports a maximum round-trip time (RTT) of 80 ms, Metro vMotion supports a RTT up to 10 ms (Enterprise Plus license).

You can split nodes in 2 ways; with or without the use of ISL’s (Inter-Switch Link). Both deployment methods are covered in detail in this document.


Deployment without ISL
Nodes are directly connected to the FC switches in both the local and remote site, without traversing an ISL. Passive WDM devices (red line) can be used to reduce the number of links. You’ll need to equip the nodes with “colored” long distance SFP’s.

SVC no ISLSource

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Stretched Cluster on IBM SVC (Part 1)

This is part 1 of the VMware Stretched Cluster on IBM SVC blogpost series.

PART 1     (intro, SVC cluster, I/O group, nodes)
PART 2     (split I/O group, deployment, quorum, config node)
PART 3     (HA, PDL, APD)

 

ibm-pc

Last year I was the primary person responsible for implementing a new storage environment based on IBM SVC and V7000 and building a VMware Stretched Cluster (a.k.a. vSphere Metro Storage Cluster) on top of that. I would like to share some of the experience I gathered, caveats I encountered and other points of interest. This is by no means a complete implementation guide (go read the Redbook 😉 ). I’ll discuss some of the implementation options as well as failure scenario’s, advanced settings and some other stuff I think is interesting. Based on the content, this will be a multi-part (probably 3) blog post.

Stretched Cluster versus Site Recovery Manager
If you’re unfamiliar with the concepts Stretched Cluster and SRM, I suggest you read the excellent whitepaper “Stretched Clusters and VMware vCenter Site Recovery Manager“, explaining which solution best suits your business needs. Another good resource is VMworld 2012 session INF-BCO2982, with the catchy title “Stretched Clusters and VMware vCenter Site Recovery Manager: How and When to Choose One, the Other, or Both“, however you’ll only be able to access this content if you’ve attended VMworld (or simply paid for a subscription).

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