Running CoreOS on Fusion

I wanted to play around with CoreOs and Docker a bit so I went to the CoreOS website but unfortunately they do not provide an OVF or OVA download. The CoreOS website doesn’t really explain how to do this, they do show how to do it for ESXi where they show how to create an OVF/OVA. I figured I would do a quick write-up on how to get the latest version up and running quickly in Fusion, without jumping through hoops.

  • Download the latest version here: (~180MB)
  • Unzip the file after downloading
  • If you look in the folder you will see a “.vmx” file and a “.vmdk” file
  • Move the whole folder in to the “Virtual Machines” folder under “Documents”
  • Now simply right click the VMX file and “open” it
  • You may be asked if you want to upgrade the hardware, I recommend doing this
  • Boot

After you are done booting you can “simply” connect to is as follows:

  • Look at the VM console for the IP Address
  • Now change your directory to the folder where the virtual machine is stored as there should be a key in that folder
  • Now run the following command, where is the IP of the VM in my environment:
    ssh -i insecure_ssh_key core@

Note that the key is highly insecure and you should replace it of course. More details can be found here.

PS: Dear CoreOS, please create an OVA or OVF… It will make life even easier for your customers.

vSphere 5.5 U1 patch released for NFS APD problem!

On April 19th I wrote about an issue with vSphere 5.1 and NFS based datastores APD ‘ing. People internally at VMware have worked very hard to root cause the issue and fix it. Log entries witnessed are:

YYYY-04-01T14:35:08.075Z: [APDCorrelator] 9414268686us: [] Device or filesystem with identifier [12345678-abcdefg0] has entered the All Paths Down state.
YYYY-04-01T14:36:55.274Z: No correlator for vob.vmfs.nfs.server.disconnect
YYYY-04-01T14:36:55.274Z: [vmfsCorrelator] 9521467867us: [esx.problem.vmfs.nfs.server.disconnect] 12345678-abcdefg0-0000-000000000000 NFS-DS1
YYYY-04-01T14:37:28.081Z: [APDCorrelator] 9553899639us: [] Device or filesystem with identifier [12345678-abcdefg0] has entered the All Paths Down Timeout state after being in the All Paths Down state for 140 seconds. I/Os will now be fast failed. 

More details on the fix can be found here:

Why Queue Depth matters!

A while ago I wrote an article about the queue depth of certain disk controllers and tried to harvest some of the values and posted those up. William Lam did a “one up” this week and posted a script that can gather the info which then should be posted in a Google Docs spreadsheet, brilliant if you ask me. (PLEASE run the script and lets fill up the spreadsheet!!) But some of you may still wonder why this matters… (For those who didn’t read some of the troubles one customer had with a low-end shallow queue depth disk controller, and Chuck’s take on it here.) Considering the different layers of queuing involved, it probably makes most sense to show the picture from virtual machine down to the device.

queue depth

In this picture there are at least 6 different layers at which some form of queuing is done. Within the guest there is the vSCSI adaptor that has a queue. Then the next layer is VMkernel/VSAN which of course has its own queue and manages the IO that is pushed to the MPP aka muti-pathing layer the various devices on a host. On the next level a Disk Controller has a queue, potentially (depending on the controller used) each disk controller port has a queue. Last but not least of course each device (i.e. a disk) will have a queue. Note that this is even a simplified diagram.

If you look closely at the picture you see that IO of many virtual machines will all flow through the same disk controller and that this IO will go to or come from one or multiple devices. (Typically multiple devices.) Realistically, what are my potential choking points?

  1. Disk Controller queue
  2. Port queue
  3. Device queue

Lets assume you have 4 disks; these are SATA disks and each have a queue depth of 32. Total combined this means that in parallel you can handle 128 IOs. Now what if your disk controller can only handle 64? This will result in 64 IOs being held back by the VMkernel / VSAN. As you can see, it would beneficial in this scenario to ensure that your disk controller queue can hold the same number of IOs (or more) as your device queue can hold.

When it comes to disk controllers there is a huge difference in maximum queue depth value between vendors, and even between models of the same vendor. Lets look at some extreme examples:

HP Smart Array P420i - 1020
Intel C602 AHCI (Patsburg) - 31 (per port)
LSI 2008 - 25
LSI 2308 - 600

For VSAN it is recommended to ensure that the disk controller has a queue depth of at least 256. But go higher if possible. As you can see in the example there are various ranges, but for most LSI controllers the queue depth is 600 or higher. Now the disk controller is just one part of the equation, as there is also the device queue. As I listed in my other post, a RAID device for LSI for instance has a default queue depth of 128 while a SAS device has 254 and a SATA device has 32. The one which stands out the most is the queue depth of the SATA device, only a queue depth of 32 and you can imagine this can once again become a “choking point”. However, fortunately the shallow queue depth of SATA can easily be overcome by using NL-SAS drives (nearline serially attached SCSI) instead. NL-SAS drives are essentially SATA drives with a SAS connector and come with the following benefits:

  • Dual ports allowing redundant paths
  • Full SCSI command set
  • Faster interface compared to SATA, up to 20%
  • Larger (deeper) command queue [depth]

So what about the cost then? From a cost perspective the difference between NL-SAS and SATA is for most vendors negligible. For a 4TB drive the difference at the time of writing on different website was on average $ 30,-. I think it is safe to say that for ANY environment NL-SAS is the way to go and SATA should be avoided when possible.

In other words, when it comes to queue depth: spent a couple of extra bucks and go big… you don’t want to choke your own environment to death!

vCenter Availability and Performance survey

One of the VMware product managers asked me to share this with you guys and ask you to please take the time to fill out this vCenter Server availability and performance survey. It is a very in-depth survey which should help the engineering team and the product management team making the right decisions when it comes to scalability and availability. So if you feel vCenter scalability and availability is important, take the time to fill it out!

Automation is scary!

Last couple of months I noticed something which led me to believe that automation is scary… And I am sure that my friends William Lam, Luc Dekens and Alan Renouf are on top of their desk right now and yelling at me but when they finished reading this post I am sure they agree.

I have been blogging for a while and when I started blogging, more than 6 years back, I posted a couple of simple scripts I wrote. The scripts allowed you to do simple things like checking the available disk space, finding snapshots, committing snapshots, find unregistered VMs, clean unregistered VMs etc. Basically the kind of scripts I used when I was a consultant to clean up the mess I typically found a couple of months after a new environment was deployed.

Many people downloaded these scripts and ran them in their environment, back then I didn’t think much of it to be honest… I mean I wrote some simple scripts and people were using those to their advantage right? Well… yes and no. Yes I did write scripts, and yes they were using them to their advantage and yes they were simple for sure. (I am not a scripting god.) So what is the problem then?

The problem is simple, 6+ years after I wrote those scripts I still receive questions about how to use them. Now note this: Those scripts were written when ESX was still the core hypervizor to use. Those scripts were written to run within the service console. Those scripts were written for ESX version 2.5.x and 3.x. Today we use ESXi and majority of folks will be on version 5.x. More than 6 years have passed, but people are still downloading them and putting them in places where they don’t belong and try to run them; without thinking about.

That is why I think Automation is Scary! (Yes in this case capital S is warranted.) If you are looking to automate operational procedures / tasks. (Automation is NOT a replacement for proper operational procedures by the way!) If you are looking to create or re-use (simple) reporting scripts, or scripts which execute simple tasks for you make sure you:

  1. Read the script, and make sure you understand every line of code
  2. Test the script in a test environment
  3. Check for which version the script was written and validate it against your version
  4. Don’t trust ANYONE blindly, and when changes are introduced in your environment or to the script go to step 1 again!

Automation isn’t really scary of course, automation can make your life easier. Just make sure you don’t become that person who has to restore 80 VMs because that script which was cleaning up unregistered VMs unintentionally deleted production VMs… Make sure you understand what your scripts are doing and assess the potential risk.