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April, 2014

Impact of VSAN on Memory Utilization in a Home Lab

This weekend I’m working on standing up and configuring VMware NSX in my home lab.  While doing so I started to cut down the amount of RAM assigned to some VMs to free up resources.  This got me wondering…  “How much RAM does VSAN use in a home lab?”.  It’s well understood that VSAN does have an impact on the hosts but I was curious to see just how much in a small environment and if it was worth disabling, as I only use it for feature testing and not for primary storage.  My primary storage is on a Synology DS1813+ full of Kingston E100 SSDs.  Fast. 🙂

My lab consists of three hosts and a total of four disk groups in VSAN.  They are:

  • 1 x FusionIO ioDrive2 785GB Card and 2 x 7200RPM SATA
  • 1 x FusionIO ioDrive2 785GB Card and 2 x 7200RPM SATA
  • 2 x Intel S3700 100GB SSD and 2 x 7200RPM SATA (split in to two disk groups)

Note that when I tested this there were no VMs being stored on or running from the VSAN datastore.  No VMs were vMotioned between hosts during testing.

Here is before I enabled VSAN.

Cluster Resources Before VSAN
Cluster Resources Before VSAN

Before VSAN the cluster had 39.98GB free memory.

Before VSAN on a Host
Host Resources Before VSAN

On the host I had:

  • 13.96GB free memory
  • 5,848MB used by the system

Now let’s enable VSAN and see how it compares.


Cluster Resources After VSAN
Cluster Resources After VSAN

As you see after VSAN there was 35.85GB of free memory in the cluster.  That is 4.13GB used by VSAN total.

Host Resources After VSAN
Host Resources After VSAN

On the same host as above the resources changed to:

  • 12.56GB free memory
  • 7,282MB used by the system

This host lost 1,434MB of RAM to VSAN.  Out of curiosity I wondered if the host with two disk groups had to give up more so I tested that too.

  • Before:  18.77GB free total and 3,846MB used by System
  • After:  17.37GB free total and 5,279MB used by System

That’s a difference of 2,003MB of RAM so it does seem to cause a higher impact.

While this isn’t a huge amount of memory it is something to keep in mind if you’re using VSAN in a home lab, especially if you’re hosts have 16GB or less of RAM in them.  Even with 32GB hosts like I have it’s worth thinking about should you start loading up a lot of VMs.

EDIT:  This post started a bit of conversation on Twitter so Wade Holmes put up a post with a table showing memory minimums needed for different disk groups.  Very handy.



4 thoughts on “Impact of VSAN on Memory Utilization in a Home Lab”

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