At the heart of VMware’s software defined storage (SDS) offering is VMware vSAN. Software defined storage offerings such as VMware vSAN are helping to solve many of the traditional storage issues that have existed for years such as storage silos and vendor specific storage implementations that require enlisting special storage teams to handle storage provisioning. Software defined storage removes the dependency from specialized hardware and repositions it into the software layer. This allows for using commodity hardware and easily allows scaling out environments in a very cost-effective way. However, VMware vSAN is a different animal when it comes to the storage side. Let’s take a look at VMware vSAN Backup Considerations as they relate to the architecture of VMware vSAN.

VMware vSAN Architecture

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First, let’s look at VMware vSAN architecture to understand how vSAN storage technology works. VMware vSAN is certainly a departure from a standard VMFS formatted LUN attached to an ESXi host. It is NOT a Virtual Storage Appliance (VSA). Rather than being RAID in the traditional sense, VMware vSAN is a distributed RAID architecture where the RAID information is distributed across the nodes or we could say is RAID over the underlying network. In the vSAN cluster, this means the vSAN virtual disks can be spread across multiple underlying physical disks and vSAN hosts in the cluster.

VMware vSAN supports the following RAID levels:

  • RAID 1 – synchronous mirroring of data – This allows replica copies of the VM storage objects to be copied equaling the number of failures to tolerate that is configured on the VM’s storage policy

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    VMware vSAN failures to tolerate configuration

  • RAID 5 and RAID 6 – With vSAN 6.2, the RAID types were expanded to include RAID 5 and RAID 6 with the ability to give preference to capacity. Instead of the synchronous mirroring mechanism, RAID 5 and RAID 6 vSAN makes use of distributed parity where the parity information in RAID 5 is spread across (3) ESXi host disks as well as one additional ESXi host. In RAID 6 it is spread across (4) ESXi host disks and (2) additional ESXi hosts. RAID 5 needs (4) ESXi hosts and RAID 6 requires (6) ESXi hosts

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Choosing the Failure tolerance method including RAID levels for performance or capacity

VMware vSAN brings a unique approach to storing virtual machine data in that it makes use of object storage as opposed to the more traditional VMware VMFS formatted LUN. VMware vSAN storage is made up of objects and components. What are the objects contained on the vSAN datastore?

  • VM home directory – “Namespace” directory – formatted with VMFS to allow a VMs configuration files to be stored and is mounted under the root directory on vsanDatastore
  • VM swap object – This exists if the VM is powered on
  • VMDKs
  • Snapshot delta disks
  • Snapshot memory

Components are simply small subcomponents of the above objects that are stored in a physical disk group. VMware vSAN will break down a large component into smaller components to help balance capacity consumption across disks and to help optimize rebuild and resynchronize activities which leads to much better overall efficiency. The vSAN witness component is another component that is a point of interest as it is the component that helps to establish quorum or majority in the event of a failure in the vSAN cluster.

This unique approach with VMware vSAN of using a storage solution based on object storage has several advantages when it comes to policy, availability, and scalability.

  • Storage Based Policy Management – With traditional storage such as a LUN or volume that is backed with RAID, it is only able to provide a specific level of performance and availability. Each LUN or volume is relegated to providing one level of service regardless of the workloads. With VMware vSAN, the policy is per VM and even per VMDK levels of service that can be controlled via the SPBM features in vSAN
    • By default, vSAN objects are thin-provisioned with implicit object space reservation of 0%
  • High Availability – Utilizing objects, fault domains, and rebuild/resynchronize, VMware vSAN provides a highly available solution
  • Scalability – VMware vSAN offers better scalability as there is per VM locking, and no issues as the number of VMs grow as well as no global namespace transactions. It allows for easily scaling up as well as scaling out, all from within the vCenter Server vSphere web client interface

VMware vSAN Backup Considerations

What considerations need to be made when it comes to backing up VMware vSAN backed virtual machines? The great thing about VMware vSAN is the traditional VMware vSphere Storage and Data Protection APIs are compatible with virtual machines running on top of vSAN. This means these same APIs can interact with vSAN the same as with VMFS and NFS datastores.

Backup technologies supported with VMware vSAN

  • NBD (network block device) and NDB SSL (encrypted) transport
  • HotAdd functionality – Allows devices to be added while the virtual machine is running
  • vSAN offers significantly more efficient snapshot creation due to a native vSAN snapshot format that has significantly lower overhead. Additional improvements with snapshot merge in 6.0 and above allow for additional snapshot performance enhancements
  • VMware vSAN can take advantage of the native vSphere Replication technology
  • VAIO (vSphere APIs for I/O Filtering) – supported by vSAN

The following is not supported with VMware vSAN:

  • San Transport – VMware vSAN uses modes that are not compatible with SAN transport and is disabled if the virtual disk library detects the presence of vSAN

There are other important considerations to keep in mind when restoring virtual machines to VMware vSAN. As mentioned above, VMware vSAN makes use of Storage Policy-based Management or SPBM. Make sure your VMware backup solution is able to support SPBM during recovery. Otherwise, the virtual machine can be recovered, however, the storage policy will need to be reapplied after the virtual machine is restored

Concluding Thoughts

VMware vSAN is exciting storage technology that offers organizations a much more scalable, manageable, and native storage solution that is available inherently with vSphere. VMware vSAN benefits greatly from the underlying storage architecture that is based on an object storage solution. This allows vSAN to make use of Storage Policy-based Management that allows extremely granular control of availability and the performance of the virtual machine residing on a vSAN datastore down to the VMDK level. There are VMware vSAN backup considerations that need to be made when thinking about data protection and VMware backups. VMware administrators need to make sure they have a support statement for VMware vSAN from their backup software vendor. Backup solutions such as Vembu BDR Suite v3.9 include support for VMware vSAN. It is important to understand backup technologies such as SAN transport that are not supported with vSAN.

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