In the DAS model, if the server is down or experiencing problems, users cannot store and access data.  Surveillance mages cannot be retrieved or stored.  If the organization grows and needs new servers, storage for each server must be administered separately.  That can get quite messy.  They will want to move to a networked storage solution as quickly as possible.

Thankfully, organizations transitioning to networked storage can protect their investment in their legacy DAS system.  The most popular option is to place it on the network via a bridge device.  As a result, the current storage resource can be used in a new networked infrastructure without incurring the immediate costs of networked storage.  Once the transition is made, DAS can still be used locally to store less critical data, such as keeping images from the cameras watching over the building’s hallways.

2.  NAS: File-Level Data Sharing Across the Enterprise.  For those systems that must store a large amount of images for many days, NAS is a good option.  Network-attached storage (NAS) is a special purpose device, comprised of both hard disks and management software.  It is 100 percent dedicated to serving files over a network. As a result, NAS relieves the server of storage and file serving responsibilities and provides a lot more flexibility in data access by virtue of being independent.

NAS and storage area networks (SAN) are sometimes competitive when creating a system but just as likely to become part of a NAS/SAN convergence scheme.  High reliability features, such as RAID and hot swappable drives and components (covered below), are standard even in lower end NAS systems, while midrange offerings provide enterprise data protection features such as replication and mirroring for business continuance.

NAS is an attractive investment that provides tremendous value, considering that the main alternatives are adding new servers, which is an expensive proposition, or expanding the capacity of existing servers, a long and arduous process that is usually more trouble than it's worth. NAS systems can provide many terabytes of storage in high-density form factors, making efficient use of data center space. 

3.  SANs: High Availability for Block-Level Data Transfer.  A storage area network (SAN) is a dedicated, high-performance storage network that transfers data between servers and storage devices, separate from the local area network. With their high degree of sophistication, management complexity and cost, SANs are traditionally implemented for mission-critical applications in the enterprise space.

In contrast to DAS or NAS, which are optimized for data sharing at the file level, the strength of a SAN lies in its ability to move large blocks of data or images. This is especially important for bandwidth-intensive applications such as large IP/megapixel camera system recording. The distributed architecture of a SAN also enables it to offer higher levels of performance and availability than any other storage medium. By dynamically balancing loads across the network, SANs provide fast data transfer while reducing latency and server workload.  Large numbers of users can simultaneously access images without creating bottlenecks on the local area network and servers.

SANs ensure predictable performance and 24x7 data availability and reliability. They also offer excellent scalability for large enterprises that anticipate significant growth in surveillance storage requirements.  And unlike DAS, excess capacity in SANs can be pooled, resulting in a very high utilization of resources.

There has been much debate in recent times about choosing SAN or NAS in the purchasing decision, but the truth is that the two technologies can prove quite complementary. Today, SANs are increasingly implemented in conjunction with NAS.

With SAN/NAS convergence, companies can consolidate block-level and file-level data on common arrays.