vSphere 5.5 VSAN, Introducing Your New Storage Vendor VMware

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The best VMworld 2013 announcement for me has to be the new vSphere Virtual SAN (VSAN). I think this new vSphere feature will change the hyper-converged and storage market FOREVER. VMware created distributed storage on the VMkernel layer. Your right… NO Storage Appliance VM needed per ESXi host.

This storage service runs inside the VMkernel! also VMware has added vSphere Flash Read (and write through) Cache on the VSAN (vFlash)

vSphere Virtual SAN: Radically Simple Storage

Key Features:

  • imagePolicy-driven per-VM SLA
  • vSphere & vCenter integration
  • Scale-out (3 – 8 hosts)
  • Built-in resiliency
  • SSD caching
  • Converged Compute & Storage


  • Radically Simple Storage designed for Virtual Machines
  • Fast, Resilient & Dynamic
  • Lower TCO for comparable performance


  • Hybrid storage system which leverages local SSD’s as a cache and aggregates local HDD’s to provide a distributed data store for VM consumption
  • Distributed object-based RAIN architecture provides no single point of failure
  • Fully integrated with vCenter, HA, DRS, vMotion
  • Scale-Out Storage: 3-8 nodes in 1.0, >8 planned for near future

VSAN Hardware Requirements


  • Not every node in a VSAN cluster needs to have local storage.
  • Hosts with no local storage can still leverage distributed datastore

Configure VSAN


  • If VSAN is configured in Automatic mode, all empty local disks are claimed by VSAN for the creation of the distributed vsanDatastore
  • If VSAN is configured in Manual mode, the administrator must manually select disks to add the the distributed vsanDatastore by creating Disk Groups.

VSAN is Fully Integrated with vSphere

All the management tasks pertaining to the installation, configuration & monitoring of VSAN will be done only from the vSphere Web Client.


After VSAN is Turned on, a single vsanDatastore is created, using storage from multiple hosts and multiple disks in the cluster.


All VM I/O is directed to the SSD. Writes are later destaged to HDD. If the requested read block is not in cache, the request is directed to HDD

vsanDatastore Availability


The virtual machine storage objects (VM Home, VMDK, delta, swap) may be distributed across the hosts and disks in the VSAN cluster. VMs may have a replica copy for availability or stripe for HDD performance.image

VM Storage Policies

  • VM Storage Policies are built in advance of VM deployment to reflect the requirements of the applications running in the virtual machine.
  • The policy is based on the VSAN capabilities.
  • Thus the policy comprises of only VSAN capabilities.
  • The appropriate policy is selected for the VM at deployment time (based on VM requirements)

VM Storage Policy – Terminology

Capabilities are what the underlying storage surfaces up to vCenter and what it is capable of offering.Requirements are what we want for our VM/application. Requirements can only be used against available capabilities.VM Storage Policies are where we put our Virtual Machine’s requirements, in the form of capabilities.

VSAN Support and Capabilities

  • Number of disk stripes per object:
    The number of HDD’s across which each replica of a storage object is distributed. Only used if cache not satisfying performance need Flash Read Cache misses need to get serviced from HDD.
  • Number of failures to tolerate:
    For  “n” number of failures to be tolerated by the cluster, “n+1” copies of the storage object (virtual machine files) are created and at least “2n+1” hosts are required to be in the cluster.
  • Object space reservation:
    % of the logical size of storage object, including snapshots, that should be reserved (thick provisioned). Rest of object is thin.
  • Flash read cache reservation:
    Flash capacity reserved as read cache for the storage object. Specified as a percentage of the logical size of the object
  • Force provisioning:
    If non-zero, object will be provisioned even if the policy requirements are not satisfied by the vsanDatastore.

Decisions when creating a VM Storage Policy

  • Do I want availability for this VM?
    If yes, then Number of failures to tolerate should be a capability in the policy.
  • Do I want additional performance (above the default) for this VM?
    If yes, then Number of disk stripes and Flash read cache reservation are capabilities that can be used for performance purpose.
  • Do I want the VM to be thickly provisioned?
    If yes, then Object space reservation should be a capability in the policy.
  • Do I want the VM deployed even if VSAN cannot meet the policy?
    If yes, then Force provisioning should be a capability in the policy.

VM Storage Policy Best Practices

  • Number of Disk Stripes per object should be left at 1 unless the the IOPs requirement of the VM is not being met by the SSD cache.
  • Flash Read Cache Reservation should be left at 0 unless there is a specific performance requirement to be met by the VM. With no reservation, the VSAN scheduler will take care of fair cache allocation.
  • Proportional Capacity should be left at 0 unless thick provisioning of virtual machines is required. By default, VMs deployed on VSAN are thin.
  • Force Provisioned VMs will be brought to compliance when the resources become available. However, you may not have the desired availability requirements for the VM until that time.

VSAN Interoperability

VSAN is fully integrated with many of VMware’s storage and availability features.


Not Applicable


  • VM snapshots
  • vSphere HA
  • DRS
  • vMotion
  • Storage vMotion
  • SRM/VR
  • SIOC
  • Storage DRS
  • DPM
  • Horizon View
  • vCloud Director
  • 62TB VMDKs

My Take

I have setup VSAN in my lab and it was amazingly simple. Try it out for yourself when VMware will release the vSphere 5.5 code. I think this will definitely disturb the Storage Space. Especially when it scales >8 hosts and even >32 hosts…


Last but not least, why not get involved in the VSAN beta. All the details are here, and it will provide you with an opportunity to provide direct feedback on VSAN (plus there are a couple of prizes for the first sign-ups)