Yellow Bricks

by Duncan Epping

Archives for 2009

VMware vLaunchpad top 10 blogs grows to top 20 blogs

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Eric Siebert has tweaked his vLaunchpad. Instead of a top 10 Blogs he changed it to a top 20 Blogs because of the enormous amount of high quality blogs these days. I’m proud that I’m still number one on Eric’s list, heck I’m proud to even be part of the list with people like Mike Laverick, Scott Lowe, Jason Boche, Mike D, Chad Sakad, Tom Howarth and Christopher Hoff…. I guess I could name every single one on the list cause they all write amazing articles. I suggest you go to the vLaunchpad. Set it as your homepage and make sure to check out the top 20 blogs at least, they are most definitely worth your time!

Again, thanks Eric for your support, compliments and thanks for heading all the traffic into this direction!

An 8MB VMFS blocksize doesn’t increase performance?

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VMFS Blocksizes have always been a hot topic regarding storage performance. It has been discussed by many including Eric Siebert on ITKE and Gabe also opened a topic on VMTN and he answered  his own question at the bottom. Steve Chambers wrote a great article about Disk Alignment and Blocksize on VI:OPS which also clearly states:”the VMFS block size is irrelevant for guest I/O.” Reading these articles/topics we can conclude that an 8MB blocksize opposed to a 1MB blocksize doesn’t increase performance.

But, is this really the case? Isn’t there more to it than meets the eye?

Think about thin-provisioning for a second. If you create a thin provisioned disk on a datastore with a 1MB blocksize the thin provisioned disk will grow with increments of 1MB. Hopefully you can see where I’m going. A thin provisioned disk on a datastore with an 8MB blocksize will grow in 8MB increments. Each time the thin-provisioned disk grows a SCSI reservation takes place because of meta data changes. As you can imagine an 8MB blocksize will decrease the amount of meta data changes needed, which means less SCSI reservations. Less SCSI reservations equals better performance in my book.

For the current VI3 environments, besides VDI, I hardly have any customers using thin provisioned vmdk’s. But with the upcoming version of ESX/vCenter this is likely to change because the GUI will make it possible to create thin provisioned vmdk’s. Not only during the creation of vmdk’s will thin provisioned disks be an option, but also when you initiate a Storage VMotion you will have the option to migrate to a thin provisioned disk. It’s more than likely that thin provisioned disks will become a standard in most environments to reduce the storage costs. If it does, remember that when a thin provisioned disk grows a SCSI reservation takes place and less reservations is definitely beneficial for the stability and performance of your environment.

Speed up your powershell scripts

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On the VI Toolkit blog there’s a great article for people like me. They explain how to speed up your scripts. I’m no powershell guru, and these kind of articles are more than welcome to boost my scripting skills.

In short, it comes down to these three tips:

  1. Try to load as many objects as possible into arrays beforehand. Once you’ve got them loaded you can use them as arguments to multiple calls without having to resort to potentially expensive lookups every time.
  2. Just like in sample 1 above, when you’ve loaded objects, use the objects directly rather than using their names. This is usually not hard as our cmdlets are designed to take object first-and-foremost, and names are supported just as a convenience.
  3. If you absolutely need to load a single VM object by name, load it using the Get-VMFast function below. While this approach can certainly help, it’s not nearly as good as using the other two techniques mentioned above.

Head over to the VI Toolkit blog and start reading.

mbrscan, mbralign and RCU

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A while back I wrote an article on checking your disk alignment and even changing the disk alignment from the service console. Since then a lot of people asked me for the exact link, because I don’t have a now.NetApp.com account I wasn’t able to provide it. Today I received an email from the developer, Eric Forgette, with a link to a community article which contains links to both tools, mbralign and mbrscan.

Eric is also the one who developed RCU(Rapid Cloning Utilities). I just watched the demo video on youtube. In short: It’s a vCenter pluging which enables you to deploy hundreds of VDI desktops by utilizing the capabilities of the array. Keith Aasen wrote a blog article on this plugin which has some more details. I guess with the vStorage API coming up we can expect more vendors to add storage capabilities to the vCenter GUI, think snapshots / clones and more…

HA enhancements, exploring the next version of ESX/vCenter

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Let’s start with a screenshot:

These are the properties of an HA cluster, as you can see there are two sections that changed:

  1. “Enable Host Monitoring” is a brand new feature. Anyone who did network maintenance while HA was enabled knows why this feature will come in handy. Those that didn’t: Isolation response! If ESX is unable to send or receive it’s heartbeat and can’t ping it’s default isolation response address it will shutdown all VM’s. To avoid this behavior you can switch of HA for a specific host with this new feature. In just four words: Maintenance mode for HA.
  2. Besides the amount of host failures a cluster can tolerate you can also specify a percentage. With the “host failures” option VMware uses the highest values of CPU and Memory reservations to calculate the amount of slots. (For more on slot / slot size read the Resource Management Guide for ESX 3.5) With the new option “Percentage of cluster resources” this isn’t the case. This new option uses the actual reservation of the VM and calculates the total percentage of resources used based on these calculations. If no reservation have been made it uses the default 256Mhz / 256MB reservation. In other words, you will be more flexible and will get a higher consolidation ratio. If the default reservation values are to low you can always use the advanced options to increase it. Another new option is “specify a failover host”. This option can be compared to “das.defaultfailoverhost”. The good thing about this option is that the designated host will be used for fail-over only. DRS will not migrate VM’s to this host, and it’s not possible to start VM’s on this host.