Yellow Bricks

by Duncan Epping

Storage

VMworld #NotSupported lightning talk slides – Hacking SRM

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I presented this 15 minute talk at VMworld about hacking SRM or actually hacking the Storage Replication Adapter which is part of SRM. I noticed William Lam shared his slides so I figured I would do the same. This slidedeck was based on two articles I did a while back around hacking the SRA, you might want to read them as well. ( 1 , 2 )

I hope they are useful. Once again, thanks to Randy Keener for coming up with this excellent idea and thanks to the brownbag guys for helping hosting this great initiative. Lets hope we will see more of this next year at VMworld,

Say goodbye to the “Transfer LUN” aka “Swing LUN” aka “Stepping Stone”

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Every once in a while I go through some articles and see if they need to be revised or not. As there are over 1400 articles on yellow-bricks.com that is not an easy task, I can tell you that. Today I stumbled on this article I wrote early 2010. This article discussed the use of a “swing lun” to limit the amount of LUNs masked to a single host. Let me copy/paste the part that I want to revise:

In my design I usually propose a so called “Transfer Volume”. This Volume(NFS or VMFS) can be used to transfer VMs to a different cluster. Yes there’s a slight operational overhead here, but is also reduces overhead in terms of traffic to a LUN and decreases the chance of scsi reservation conflicts etc.

Here’s the process:

  1. Storage VMotion the VM from LUN on Array 1 to Transfer LUN
  2. VMotion VM from Cluster A to Cluster B
  3. Storage VMotion the VM from Transfer LUN to LUN on Array 2

Of course these don’t necessarily need to be two separate arrays, it could just as easily be a single array with a group of LUNs masked to a particular cluster. For the people who have a hard time visualizing it:

I guess this is a great example of why you need to revise your design with every release… This used to be a valid workaround to limit the amount of LUNs attached to a Cluster while maintaining the flexibility to move between clusters using Storage vMotion and vMotion. With vSphere 5.1 that is no longer needed now that we have enhanced functionality for vMotion. (Frank has an awesome vMotion deepdive… read it) Make sure to update your design and make the needed changes to your infrastructure if and when required…

Enabling PDL enhancements in a non-stretched environment?

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I received two questions on the same topic last week. The question was around using the PDL enhancements in a non-stretched environment… does it make sense? The question was linked to a scenario where for instance a storage admin makes a mistake and removes access for a specific host to a LUN. For those who don’t know what a PDL is read this article, but in short it is a SCSI sense code issued by an array when it believes storage will be permanently unavailable.

First of all, the vSphere HA advanced option “das.maskCleanShutdownEnabled” is enabled by default as of vSphere 5.1. In other words, HA is going to assume a virtual machine needs to be restarted when it is powered and isn’t able to update the config files. (Config files contain the details about the shutdown state normally, was it an admin initiated shutdown?)

Now, one thing to note is that “disk.terminateVMOnPDLDefault” is not on by default. If this setting is not explicitly enabled then the virtual machine will not be killed and HA won’t be able to take action. In other words, if your storage admin changes the presentation of your LUNs and removes a host accidentally the virtual machine will just sit there without access to disk. The OS might fail at some point, your application will definitely not be happy, but this is it.

To answer the question, yes even in a non-stretched environment it makes sense to enable both disk.terminateVMOnPDLDefault and das.maskCleanShutdownEnabled. Virtual machines will be automatically restarted by HA if they are killed by the VMkernel when a PDL has been detected.

Back to Basics: Using the vSphere 5.1 Web Client to configure iSCSI

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In this article I will take you through the steps required to setup iSCSI using the vSphere 5.1 Web Client. In most iSCSI environment the VMware software iSCSI adapter is used, so that is what I will use. I had already setup a storage VMkernel NIC in one of my previous post, read that if you haven’t yet. Adding a software adapter can be done in a couple of simple steps:

  • On the “Manage” section of your host click on “Storage”
  • Click the green “plus” and select “Software iSCSI adapter”
  • Click “OK”
  • Now a new adapter will be added to the “Storage Adapters” list

[Read more…] about Back to Basics: Using the vSphere 5.1 Web Client to configure iSCSI

Back to Basics: Using the vSphere 5.1 Web Client to add an NFS share to all hosts

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If you look at the following workflow you know why I am starting to love NFS more and more… Adding an NFS datastore was easy with 5.0 (and prior) but with 5.1 it is even easier. Just a couple of steps to add an NFS datastore to your cluster: