A disk data format is an agreed upon standard method of writing data that has been established for information in a redundant array of independent disks (RAID). In essence, a disk data format is a list of instructions that dictate certain aspects of writing data to a disk so the information contained on the disk can be retrieved by another program or piece of hardware, even if it is unrelated to the program that originally placed the data on the disk. Although the term can be generically applied to all disks, it is specifically used when talking about a RAID storage system and is an integral part of the specifications for RAID systems that are followed by most industries and manufacturers. Without a set disk data format for reading and writing data, disparate systems would be unable to work together, upgrades from one RAID setup to another would be difficult or impossible, and any data that were lost on a single system would have little chance of recovery by a third-party program. The actual disk data format specification for RAID drives is maintained by the Storage Networking Industry Association (SNIA), which consists of several parties within the storage device industry that attempt to provide neutral standards so no single type of technology that conforms to the standard will be unsupported.
A RAID system is a way to distribute information across a series of different storage devices, such as hard drives. All the drives are connected to a central processor, controller or computer and treated — from the viewpoint of a user — as if they were a single drive. The information in a single file being saved to a RAID setup can be spread across several different drives. This method of implementing a storage system is generally very cost effective and can allow for several systems to simultaneously read and write data to the disks because, at any one time, multiple disks might be idle.
The disk data format defines a standard way of saving information to the RAID system. It includes information such as the structure of header records, the organization of blocks, elements to be implemented for error checking, and some common methods for redundancy. By employing the disk data format, new hardware such as additional disk drives can be easily added to a RAID setup with the knowledge that they can be seamlessly integrated regardless of the manufacturer or hardware specifics. It also means RAID hardware can be easily moved from one system to another without having to convert the disk data format that was previously used.
One very convenient aspect in using the SNIA standards is that a company can upgrade its RAID system and easily move all the existing information to the new hardware. This process, called migration, can be a potentially hazardous procedure for non-standardized hardware. Additionally, if any information is lost or corrupted on a RAID system using the correct disk data format, utility programs will have a greater chance of reconstructing a large amount of that data and avoid a catastrophic complete loss of data.