VMware vSAN Advanced Concepts – 1

This post will discuss all the vSAN concepts that are necessary for understanding and working with vSAN. The latest version vSAN 6.2 supports both All-flash and Hybrid Configurations. Depending upon what workload we are building on the environment we must choose Alll flash or Hybrid deployment. All flash can be expensive at the begining but it can produce very high performance( Max 90K IOPS) suitable for Mission Critical Applications. Lets now discuss Architecture and all the advanced concepts in VMware vSAN

vSAN Architecture :



  • vSAN is embedded in VMkernel and is activated with the licensing
  • No need to install any extra appliance
  • Overall CPU utilization is below 10%
  • Provides the shortest path for I/O
  • Removes application management overheads
  • Does not consume unnecessary resources

Diskgroup :


  • In VMware vSAN disks are consumed using a concept called Diskgroups,
  • Every Host that participates in the vSAN cluster will have to provide its own set of one or more Diskgroups
  • A minimum of three Hosts must provide disks to the vSAN cluster, How ever Hosts can also be part of vSAN cluster without providing disks to the Diskgroup
  • Maximum capacity of each Diskgroup is 8 disks including both flash(SSD) and hard drives.(SAS/NLSAS/SATA)
  • A Diskgroup is an organization of both Flash and Spinning disks with a minimum of one flash drive and maximum of 7 hard drives.
  • Maximum of 5 Diskgroups can be created per Host
  • Diskgroups can be created in Automated mode or Manual mode

Storage Based Policies Management :
SPBM is a storage policy framework built into vSphere that enables VM-centric policy driven provisioning

  • Ideally Storage Policies are provided with by the Storage vendor and we can make use of these advanced features by specifying a storage provider for every participating Host.
  • By Navigating to vCenter > Manage > Storage Providers
  • For creating new VM Storage Policy requires Rule Sets to be defined
  • Rule Sets is a group of rules that describe requirements of storage resources
  • Each Rule Set describes some quality/quantity that satisfies a requirement
  • We must use the following URL : http://<name of Hosts>:8080/version.xml in Storage providers and we will able to create new policies
  • Every Storage vendor have their own set of Rule Sets

Storage Based Policies Management in vSAN : VMware vSAN provides the following Storage Policies which describes how vSAN treats the VM’s vmdk files and by default there are five different capabilities of vSAN, it must be noted that we will not be able to create any new Storage Policies.



  1. Failures to Tolerate (FTT)
    Number of Hosts failures that can be tolerated without losing any data. The ideal formula used for calculating the total number of Hosts in FTT is 2n+1, where ‘n’ is the number of Hosts failures. eg: if we consider FTT as 1 then 2(1)+1 = 3, therefore a minimum of 3 Hosts is required to satisfy one Host failure
    Default value is 1 , Maximum value is 31
  2. Disk Stripes / Object (Performance)
    Number of hard disks that are used for writing an Object, in certain situations if we increase the number the disks that are used for writing an object it can have a positive impact performance. Most use cases default value to be used
    Default value is 1 , Maximum value is 121
  3. Object Space Reservation (For using FT)
    By default all VM’s on vSAN are Thin Provisioned, We can reserve 100% storage for a particular VM
    Default value is 0% , Maximum value is 100%
  4. Flash Read Cache (Performance)
    We can reserve some amount of flash for a particular VM, this will increase performance of the VM
    Default value is 0% , Maximum value is 100%
  5. Force Provisioning (Overrule other Policies)
    Force provision is used only in case of emergency where the VM is provisioned in spite of violating certain policies
    Default value is No

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