Yellow Bricks

by Duncan Epping

Server

Can you run all-flash with vSAN 6.2 Standard license?

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As I get the following question a lot I figured I would share the answer here as well: Can you run all-flash with vSAN 6.2 Standard license? Many of you have seen the change in licensing when 6.5 was introduced. No longer is vSAN licenses based on storage hardware used, spindles or all-flash, you can use the lowest license SKU. Which of course is great for those wanting to use 6.5, but what about those who want to stick to 6.0 U2 aka vSAN 6.2? (This also works for 6.0 and 6.1 of course, but I would highly recommend 6.2 with the latest patches!)

Well there is a way to “downgrade” your license. (I would call it convert myself, but downgrade apparently is the official term for it.) There are 3 simple steps which are described in the following KB, but copied/pasted here for your convenience:

  1. Navigate to and login in to your MyVMware portal at www.myvmware.com.
  2. Locate the page with your licenses, and then select the license to convert. Once selected, click “Downgrade License Keys” from the drop down menu.
  3. Two downgrade options will be displayed in another drop down menu. Select “Virtual SAN 6 with All Flash Add-on” to convert your existing vSAN STD licenses to a STD version that includes the all-flash add-on.

VMware User Group

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I have the pleasure to present at three VMUGs in the upcoming months I have never presented at before, heck I never been to those countries even. First coming up is the VMUG in Dubai on the 16th of February followed by two VMUGs in Australia, with the Dutch VMUG in between. Lets see which other VMUGs we can add to that list in the upcoming months.

  • 16th of February – Dubai VMUG
  • 16th of March – NL VMUG, Den Bosch, Nederland
  • 21st of March – Sydney VMUG, Australia
  • 23rd of March – Melbourne VMUG, Australia

I will (most likely) be talking about vSAN (what else), if you are interested make sure to register through the VMUG website here: https://www.vmug.com/Attend/Calendar (no details for Dubai yet).

See you there, I will make sure to bring some goodies like stickers and probably shirts (if I can order them in time).

Windows 10 not running in full resolution in VMware Fusion?

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I installed Windows 10 in a Fusion VM recently and figured I would install VMware Tools. After the installation I couldn’t get it running in a proper resolution and I was actually limited to 1152×864. Very frustrating. I tried to solve it but for whatever reason the only thing that worked was:

  • Uninstall VMware Tools
  • Restart VM
  • Install VMware Tools
  • Change resolution to desired resolution

That fixed it for me, if you had the same problem but a different solution please leave a comment!

Disk controllers for vSAN with or without cache?

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I got this question today and I thought I already wrote something on the topic, but as I cannot find anything I figured I would write up something quick. The question was if a disk controller for vSAN should have cache or not? It is a fair question as many disk controllers these days come with 1GB, 2GB or 4GB of cache.

Let it be clear that with vSAN you are required to disable the write cache at all times. The reason for this is simple, vSAN is in control of data consistency and vSAN does not expect a write cache (battery backed or not) in its data path. Make sure to disable it. From a read perspective you can have caching enabled. In some cases we see controllers where people simply set the write cache to 0% and the rest automatically then becomes read cache. This is fully supported, however our tests have shown that there’s little added benefit in terms of performance. Especially as reads come from SSD anyway typically, theoretically there could be a performance gain, but personally I would rather spend my money on flash for vSAN.

My recommendation is fairly straight forward: use a disk controller which is a plain pass through controller without any fancy features. You don’t need RAID on the disk controller with vSAN, you don’t need caching on the disk controller with vSAN, keep it simple, that works best. So if you have the option to dumb it down, go for it.

Storage capacity for swap files and TPS disabled

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A while ago (2014) I wrote an article on TPS being disabled by default in future release. (Read KB 2080735 and 2097593 for more info) I described why VMware made this change from a security perspective and what the impact could be. Even today, two years later, I am still getting questions about this and what for instance the impact is on swap files. With vSAN you have the ability to thin provision swap files, and with TPS being disabled is this something that brings a risk?

Lets break it down, first of all what is the risk of having TPS enabled and where does TPS come in to play?

With large pages enabled by default most customers aren’t actually using TPS to the level they think they are. Unless you are using old CPUs which don’t have EPT or RVI capabilities, which I doubt at this point, it only kicks in with memory pressure (usually) and then large pages get broken in to small pages and only then will they be TPS’ed, if you have severe memory pressure that usually means you will go straight to ballooning or swapping.

Having said that, lets assume a hacker has managed to find his way in to you virtual machine’s guest operating system. Only when memory pages are collapsed, which as described above only happens under memory pressure, will the hacker be able to attack the system. Note that the VM/Data he wants to attack will need to be on the located on the same host and the memory pages/data he needs to breach the system will need to be collapsed. (actually, same NUMA node even) Many would argue that if a hacker gets that far and gets all the way in to your VM and capable of exploiting this gap you have far bigger problems. On top of that, what is the likelihood of pulling this off? Personally, and I know the VMware security team probably doesn’t agree, I think it is unlikely. I understand why VMware changed the default, but there are a lot of “IFs” in play here.

Anyway, lets assume you assessed the risk and feel you need to protect yourself against it and keep the default setting (intra-VM TPS only), what is the impact on your swap file capacity allocation? As stated when there is memory pressure, and ballooning cannot free up sufficient memory and intra-VM TPS is not providing the needed memory space either the next step after compressing memory pages is swapping! And in order for ESXi to swap memory to disk you will need disk capacity. If and when the swap file is thin provisioned (vSAN Sparse Swap) then before swapping out those blocks on vSAN will need to be allocated. (This also applies to NFS where files are thin provisioned by default by the way.)

What does that mean in terms of design? Well in your design you will need to ensure you allocate capacity on vSAN (or any other storage platform) for your swap files. This doesn’t need to be 100% capacity, but should be more than the level of expected overcommitment. If you expect that during maintenance for instance (or an HA event) you will have memory overcommitment of about 25% than you could ensure you have 25% of the capacity needed for swap files available at least to avoid having a VM being stunned as new blocks for the swap file cannot be allocated and you run out of vSAN datastore space.

Let it be clear, I don’t know many customers running their storage systems in terms of capacity up to 95% or more, but if you are and you have thin swap files and you are overcommitting and TPS is disabled, you may want to re-think your strategy.