Storage considerations

Different hard disk solutions

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 detached storage solution where the storage is separate from the server running the application.

Direct Attached Storage
Detached storage: Network Attached Storage (NAS) and Storage Area Network (SAN)
RAID (Redundant Array of Independent Disks)

Direct Attached Storage (DAS)

This is probably the most common solution for hard disk storage in small to medium-sized installations. The hard disk is located in the same PC that runs the video management software (application server). Space availability is determined by the PC and the number of hard disks it can hold. Most PCs can hold 2 disks; some up to 4 disks. Each disk can be up to approximately 300 Gbyte. This gives a total hard disk capacity of approximately 1.2 TB (Terabyte).

Detached Storage:
Network Attached Storage (NAS) and Storage Area Network (SAN)

In applications where the amount of stored data and management requirements exceed the limitations of direct attached storage, a separate storage system is implemented. These systems are Network Attached Storage (NAS) and Storage Area Network (SAN).

NAS

Network Attached Storage provides a single storage device which is directly attached to a LAN and offers shared storage to all clients on the network. A NAS device is simple to install and easy to administer, providing a low-cost solution for storage requirements, but limited throughput for incoming data.

SAN

A Storage Area Network is a high speed, special-purpose network for storage, 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 over hundreds of terabytes. Centralized data storage reduces the administration required and provides a high performance, flexible storage pool for use by multi-server environments.

The difference between the two is that NAS is a storage device where the whole file is stored on one single hard disk, whereas SAN consists of a number of devices where the file can be stored block by block on multiple hard disks. This type of hard disk configuration allows for very large and scalable hard disk solutions where large amounts of data can be stored with a high level of redundancy. There are solutions of both types available for video management software.

RAID (Redundant Array of Independent Disks)

RAID is a method of arranging standard, off-the-shelf hard drives in such a way that the operating system sees them as one large logical hard disk.

There are different levels of RAID offering different levels of redundancy; from practically no redundancy at all to a full "hot swappable" mirrored solution where there is no disruption to the operation of the system and no lost data in the event of hard disk failure.

The most common RAID levels are listed in the table below.

RAID Level	Characteristics
RAID-0	Data is being striped (divided) over two or several hard disks, for improved read/write speed but no redundancy.
RAID-1	Also known as disk mirroring. At least two disks duplicate data. No striping. Both disks can be read at the same time. Write performance as for single disk storage.
RAID-5	Includes a rotating parity array, allowing all read and write operations to be overlapped. Stores parity information for reconstruction of any lost data. RAID-5 requires at least 3, and runs with up to 16 disks in the array.

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