VMworld TV, it just rocks!

VMworld TV has been around for a long time, and I truly enjoy the videos. I know what kind of work goes in to recording these episodes and the long hours these guys make, so thanks for doing this Eric, Jeremy and production/camera crew! It is awesome work, and even though I attend VMworld, and the only way to get an idea about the atmosphere at the event and the awesomeness of some of the new products VMware announced and even VMware partners announced. I wanted to embed every video in this post, but considering they recorded over 40 that ended up being a bit too much. My fav. videos are in bold, here are the titles and links:


Want a free digital copy of the vSphere Design Pocketbook?

I just noticed that PernixData is offering free copies of the vSphere Design Pocketbook. Only thing you will need to do is register here. I believe at VMworld they handed out roughly 1500 copies of these, and they have been very well received. For those who don’t know, this book was “authored by the community” with people like Frank Denneman, Cormac Hogan, Jason Nash, Eric Sloof, Vaughn Stewart and I deciding which consideration was in and which was one out. (Somehow we needed to ensure message weren’t conflicting or potentially “damaging” to an environment.)

Hopefully PernixData will have some more physical copies in Barcelona, but just in case they don’t… sign up for the free e-copy!

How do you know where an object is located with Virtual SAN?

You must have been wondering the same thing after reading the introduction to Virtual SAN. Last week at VMworld I received many questions on this topic, so I figured it was time for a quick blog post on this matter. How do you know where a storage object resides with Virtual SAN when you are striping across multiple disks and have multiple hosts for availability purposes, what about Virtual SAN object location? Yes I know this is difficult to grasp, even with just multiple hosts for resiliency where are things placed? The diagram gives an idea, but that is just from an availability perspective (in this example “failures to tolerate” is set to 1). If you have stripe width configured for 2 disks then imagine what could happen that picture. (Before I published this article, I spotted this excellent primer by Cormac on this exact topic…)

Luckily you can use the vSphere Web Client to figure out where objects are placed:

  • Go to your cluster object in the Web Client
  • Click “Monitor” and then “Virtual SAN”
  • Click “Virtual Disks”
  • Click your VM and select the object

The below screenshot depicts what you could potentially see. In this case the Policy was configured with “1 host failure to tolerate” and “disk striping set to 2″. I think the screenshot explains it pretty well, but lets go over it.

The “Type” column shows what it is, is it a “witness” (no data) or a “component” (data). The “Component state” shows you if it is available (active) or not at the moment. The “Host” column shows you on which host it currently resides and the “SSD Disk Name” column shows which SSD is used for read caching and write buffering. If you go to the right you can also see on which magnetic disk the data is stored in the column called  “Non-SSD Disk Name”.

Now in our example below you can see that “Hard disk 2″ is configured in RAID 1 and then immediately following with RAID 0. The “RAID 1″ refers to “availability” in this case aka “component failures” and the “RAID 0″ is all about disk striping. As we configured “component failures” to 1 we can see two copies of the data, and we said we would like to stripe across two disks for performance you see a “RAID 0″ underneath. Note that this is just an example to illustrate the concept, this is not a best practice or recommendation as that should be based on your requirements! Last but not least we see the “witness”, this is used in case of a failure of a host. If host would fail or be isolated from the network somehow then the witness would be used by host to claim ownership. Makes sense right?

Virtual SAN object location

Hope this helps understanding Virtual SAN object location a bit better… When I have the time available, I will try to dive a bit more in to the details of Storage Policy Based Management.

vSphere 5.5 nuggets: High Availability Enhancement

There aren’t a lot of changes in 5.5 when it comes to vSphere High Availability aka HA, but one is worth noting. As most of you are probably aware of, vSphere HA in the past did nothing with VM to VM Affinity or Anti Affinity rules. Typically for people using “affinity” rules this was not an issue, but those using “anti-affinity” rules did see this as an issue. They created these rules to ensure specific virtual machines would never be running on the same host, but vSphere HA would simply ignore the rule when a failure had occurred and just place the VMs “randomly”. With vSphere 5.5 this has changed! vSphere HA is now “anti affinity” aware. In order to ensure anti-affinity rules are respected you will need to set an advanced setting:

das.respectVmVmAntiAffinityRules - Values: "false" (default) and "true"

Now note that this also means that when you configure anti-affinity rules and have this advanced setting  configured to “true” and somehow there aren’t sufficient hosts available to respect these rules… then rules will be respected and it could result in HA not restarting a VM. Make sure to understand this potential impact when configuring this setting and configuring these rules.

vSphere 5.5 nuggets: Change Disk.SchedNumReqOutstanding per device!

Always wanted to change Disk.SchedNumReqOutstanding per device instead of per host? Well now with vSphere 5.5 you can! I didn’t know about this either, but my colleague Paudie pointed this out. Useful feature when you have several storage arrays and you need to tweak these values, now lets be clear… I do not recommend tweaking this, but in the case you need to you can now do it per device using esxcli.

Get the current configured value for a specific device:
esxcli storage core device list --device <device>

Set the value for a specific device::
esxcli storage core device set -d <device> -O <value between 1-256>.