As previously mentioned, IP surveillance does not require specialized storage solutions - it simply utilizes standard components commonly found in the IT industry. This provides lower system costs, higher redundancy, and greater performance and scalability than found in DVR counterparts.
Storage solutions depend on a PC's or server's ability to store data. As larger hard drives are produced at lower costs, it is becoming less and less expensive to store video. There are two ways to approach hard disk storage. One is to have the storage attached to the actual server running the application. The other is a storage solution where the storage is separate from the server running the application, called network attached storage (NAS) or storage area networks (SANs).
Direct server attached storage is probably the most common solution for hard disk storage in small to medium-sized IP surveillance installations (See image 1, server attached storage). The hard disk is located in the same PC server that runs the video management software. The PC and the number of hard disks it can hold determine the amount of storage space available. Most standard PCs can hold between two and four hard disks. With today's technology, each disk can store approximately 300 gigabytes of information for a total capacity of approximately 1.2 terabytes (one thousand gigabytes).
When the amount of stored data and management requirements exceed the limitations of direct attached storage, a NAS or SAN and allows for increased storage space, flexibility and recoverability.
NAS provides a single storage device that is directly attached to a Local Area Network (LAN) and offers shared storage to all clients on the network (See image 2, network attached storage). A NAS device is simple to install and easy to administer, providing a low-cost storage solution. However, it provides limited throughput for incoming data because it has only one network connection, which could become problematic in high-performance systems.
SANs are high-speed, special-purpose networks for storage, typically connected to one or more servers via fiber. Users can access any of the storage devices on the SAN through the servers, and the storage is scalable to hundreds of terabytes. Centralized storage reduces administration and provides a high-performance, flexible storage system for use in multi-server environments. In a SAN system, files can be stored block by block on multiple hard disks. Technologies such as Fiber Channel are commonly used, providing data transfers at four gigabits per second (Gbps).
This type of hard disk configuration allows for very large and scalable solutions where large amounts of data can be stored with a high level of redundancy. For example, the Kentucky Department of Juvenile Justice (DJJ) recently updated an analog tape storage system to a SAN system, allowing the department to install a greater number of cameras throughout its locations and centralize the storage of remote video feeds. The DJJ employed EMC Corp.'s Surveillance Analysis and Management Solution (SAMS) to make the video searchable. This system, which handles hundreds of cameras, is easily expanded and managed as each individual facilities' needs change.
SAN systems build redundancy into the storage device. Redundancy in a storage system allows for video, or any other data, to be saved simultaneously in more than one location. This provides a backup for recovering video if a portion of the storage system becomes unreadable. There are a number of options for providing this added storage layer in an IP surveillance system, including a Redundant Array of Independent Disks (RAID), data replication, tape backups, server clustering and multiple video recipients.
RAID -- RAID is a method of arranging standard, off-the-shelf hard drives such that the operating system sees them as one large hard disk. A RAID set up spans data over multiple hard disk drives with enough redundancy that data can be recovered if one disk fails. There are different levels of RAID - ranging from practically no redundancy, to a full-mirrored solution in which there is no disruption and no data loss in the event of hard disk failure.