Category Archives: Storage

vSAN Default Storage Policy Per vSAN Datastore

Everyday is a school day!!

I recently asked the vSAN vExpert slack channel the following: “Is there a way to set a default storage policy for a specific vSAN cluster? Use case – shared vCenter server with 10 hybrid vSAN clusters and 1 “private” customer with dedicated cluster running AF vSAN. The Private customer wants to use RAID6 but their deployment method just now does not allow the selection of a storage policy. We can’t change the default policy as the other 10 hybrid clusters are using this (and also don’t have a way to select a policy during deployment).”

Slightly embarrassingly for me that I didn’t know this but Steve Kaplan (@stvkpln) told me how to do it!

If you browse to the vSAN datastore object then Manage then general you can set the default policy for that datastore. Simples!

VM Limit per Host – VSAN

According to the VSAN maximums, there is a 100 VM limit per host in a VSAN 5.5 cluster and 200 in a VSAN 6 cluster. This seems to be a soft limit as I was recently able to deploy 999 VMs in to a 4 node VSAN 5.5 cluster (with one host acting as a dedicated HA node, so not running any compute). I got to ~333 VMs per host before I reached the 3000 component limit (which is a hard limit) on each host. The below is a screen grab of vsan.check_limits from RVC:


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VSAN 5.5 vs. VSAN 6.0 – Performance Testing

After upgrading VSAN 5.5 to VSAN 6.0 I thought it would be a good idea to run the same set of tests that I ran previously (VSAN 5.5 Performance Testing) to see how much of a performance increase we could expect.

The test was run using the same IOAnalyser VMs and test configuration, on the same hardware. The only different was the vCenter/ESXi/VSAN version.

                  Read Only   Write Only  Real World
VSAN 6 IOPs (Sum) 113,169.88  28,552.85   38,658.47
VSAN 5 IOPs (Sum) 61,964.81   5,666.06    24,228.98

The detailed test results for VSAN 6, using a “Real World” test pattern (70% Random / 80% Read) as below:


Great increase in IOPs!

More VSAN Components than Physical Disks

When running through some VSAN operational readiness tests I stumbled across an issue when simulating host failures. When there are more VSAN Components than physical disks and a host fails, the components will not be rebuilt on remaining hosts.

Firstly here is some background information about the test cluster:

  • 4 x Dell R730XD Servers
  • 1 Disk Group per server with one 800GB SSD fronting six 4TB Magnetic Disks
  • 1 Test VM with a single 1.98TB VMDK
  • Disks to Stripe set to 1 on the storage policy applied to the VM
  • Failure to Tolerate set to 1 on the storage policy applied to the VM
  • ESXi 5.5 and VSAN 5.
  • All drivers/firmware on the VSAN HCL

The VMDK Object is split into 24 components (8 x “Primary” components (each 250GB), 8 x “Copy” components (each 250GB) and 8 x “Witness” components

Note: VSAN does not really have “Primary” and “Copy” components but for the sake of the following diagrams and ease of explanation I’ll group the components this way.

As below:

More VSAN Components than Physical Disks - Failure Scenario

More VSAN Components than Physical Disks – Failure Scenario

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VSAN Health Plugin – Broken Web Client

Today I installed the VSAN Health Plugin – VSAN 6 Health Check Plugin. Unfortunately I did not RTFM (Read the… frigging… manual).

When I logged into the web client after restarting the vCenter services this is all I could see:


Turns out I didn’t install the msi using the “run as admin” option… really should have read that manual.

Cormac Hogan to the rescue VMware Blogs