Some NAS providers have this single volume functionality across multiple nodes, which are referred to in the industry as Scale-Out NAS. This flexibility makes it easy to leverage advanced VMS features such as automatic server failover, load balancing and scalability (since any server can get access to any recorded video).
A Scale-Out NAS system can provide access to the same data from any node and, thus, can scale linearly in capacity and performance. For example, an Isilon NAS cluster can provide up to 40PB in a single volume, making failover and automatic load balancing easy. All servers simply record to a single name space and no re-mappings of storage location per camera is ever required. Though data transfer rates may still be slightly higher for SANs, the gap is closing and the overall value proposition of a NAS is stronger than a SAN in almost all scenarios.
If a single enterprise class NAS is out of your budget, using a group of smaller mid-market NAS devices can be considered such as Iomega StorCenter Network Storage devices. Aimetis Symphony 6.12 offers the ability to automatically record video redundantly to more than one NAS or use recording failover functionality to record to a redundant NAS. In this case, each NAS operates independently but any server can gain access to any recorded video regardless of which NAS was used, since storage locations are nothing more than network shares.
While a NAS can be used with all Symphony redundancy configurations, a SAN can still be used if each LUN is only being accessed by one server in the farm. To be fair, there are ways of sharing storage from a block device, but this is not handled by the block storage device itself. Block storage devices are made "shareable" by using a clustered file system. This setup can be complex, making the attractiveness of this approach less appealing as the technology improvements in both
Ethernet and file storage devices have closed the performance gap dramatically. There are situations when block storage is the best choice. In single server deployments such as banking or retail, virtual machines (VM) are becoming increasingly common, with the VMS server running as a VM to reduce the number of physical servers IT needs to manage. Server virtualization offers advanced features such as high availability, or the ability to move a running VM from one host to another. Block storage is very common for virtual servers and works well, but with all server virtualization products now supporting the NFS protocol, NAS devices can provide a worthy, cost-effective alternative to fiber channel SANs for shared storage between VMs.
Finally, it is common today for storage devices to include both block storage and file storage from the same device. The EMC VNX Series is an example of a unified storage system. With unified storage, how the device is configured determines whether it behaves as block storage (SAN) or file storage (NAS). This drives home the point that this is purely a protocol or interface distinction, not one of size, capability, reliability, performance and features. Ultimately, both block or file storage can be used on your video project, but do not prematurely overlook file storage as the value proposition has significantly improved for projects of any size.
About the Author: Justin Schorn is vice president of product management for Aimetis and an expert in IP technology and video management software.