VMware VSAN features and realities
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VMware announced an all-new virtual storage area network (vSAN) in September to help fulfill its focus on software-defined storage. With vSAN currently in beta, and not yet recommended for actual production environments, there are positives and negatives that accompany using vSAN.
No matter what you might have heard about vSAN, it is certainly an innovative solution and I encourage you to invest a few minutes to find out more.
What is Virtual SAN?
VMware's Virtual SAN is a virtual storage area network and only provides storage for your vSphere virtual machines (VMs). VSAN, which is compatible with VMware's storage-policy-based management (SPBM) definition, is able to aggregate local server disks into a shared storage cluster. VSAN requires that you have at least three vSphere hosts, vSphere 5.5, and vCenter 5.5. Each host must have at least one local solid-state drive (SSD) and one local hard disk as well as a compatible disk controller. The ESXi hypervisor cannot be installed on either of those disks. The SSDs do not contribute to the size of the vSAN cluster; they are used for caching.
VSAN does not use Fibre Channel, iSCSI or NFS. Instead, vSAN uses a proprietary storage protocol for transferring data between vSphere hosts on the vSAN. VMs on hosts that are part of the vSAN will have faster access to virtual machine disk files. VSANs support VMware features like vMotion, distributed resource scheduler (DRS) and vSphere high availability (HA).
VSAN should not be confused with VMware's virtual storage appliance (VSA). VSAN is a much more advanced solution than VSA, as vSAN is built into the hypervisor.
One of the differentiators that VMware touts is how vSAN uses "policy-based management," which "streamlines storage provisioning and ongoing administration." While these storage policies have been available in the past (storage profiles/policies), it's important that they are vSAN-compatible to ensure that virtual machines receive the performance and availability levels that you, as an administrator, define. Through these storage profiles and intelligence built in to vSAN, VMware says vSAN is self-tuning and includes dynamic load balancing.
Other major benefits of using vSAN include:
- Easy installation with "two-click provisioning."
- Seamless integration into vSphere and vCenter with all configuration, management and monitoring for your storage done inside the vSphere Web Client
- High-performance read and write caching with intelligent data placement
- Hardware resiliency that can prevent data loss and VM downtime if a server in the vSAN cluster fails. VMware calls this vSAN distributed RAID.
Virtual SAN caveats
For many companies already using, or considering, an enterprise-grade SAN for their virtual infrastructure, VMware's vSAN may appear to offer similar functionality as expensive proprietary hardware. However, before you dump your old SAN, there are a few caveats you need to know about:
- VSAN is currently in beta form and, because of that, shouldn't be counted on for production VM storage.
- VMware hasn't released pricing details on vSAN, thus we can't yet verify any cost savings. VMware has said vSAN will be an additional cost with vSphere.
- VSAN only offers storage for your VMs. Dedicated servers cannot store data on the vSAN.
- VMware doesn't yet recommend replacing your physical SAN with vSAN, but does recommend using vSAN as a new storage tier in the data center for specific use cases. These use cases include storage for VM desktops, storage for disaster recovery infrastructure and storage for test and development environments. Storage for production VMs is notably missing from VMware's proposed use cases, but that will come in time.