What is RAID 5?
RAID Level 5 is a type of RAID that uses block-level striping (spreading out the blocks of each file across multiple disk drives) and block-interleaved distributed parity to spread the redundant parity information used to achieve fault tolerance across all the disks in the array. If any disk fails, the distributed parity data are used to compute the contents of the “virtual” (failed) disk. An advantage of RAID 5 is that there is no single dedicated parity disk causing a write bottleneck. A disadvantage of RAID 5 is that the capacity of the array of disks cannot be increased without rebuilding the array. RAID 5 is the most popular version of RAID. The Kaleidescape Server does not use RAID 5; it uses RAID-K.
• RAID 5 provides redundant backup of data by using a series of discs (4 in the case of the VX-600) where data is written across all discs. If one disc fails, the data is not lost as it is stored across the remaining 3 discs. You should replace the failed disc ASAP because if a second disc fails, you will loose data.
RAID 5 – Block-level data striping with distributed parity. A Good Compromise RAID 5 stripes data across multiple disks. RAID 5, however, adds a parity check bit to the data. This slightly reduces available disk capacity, but it also means that the RAID array continues to function if a single disk fails. In the event of a disk failure, you simply replace the failed disk and keep going. The tradeoffs with RAID 5 are a small performance penalty in write operations and a slight decrease in usabable storage space. • Minimum number of drives: 3 • Strengths: Best cost/performance for transaction-oriented networks; Very high performance, very high data protection; Supports multiple simultaneous reads and writes; Can also be optimized for large, sequential requests. • Weaknesses: Write performance is slower than RAID 0 or RAID 1.
Well, let us first start with the lower numbers. RAID 0 is what is called performance RAID. What you do is take two or more drives and “stripe” them together so they act as ONE DRIVE. “Striping” essentially means you format multiple hard drives together as one large “virtual” hard drive for your system.” For example, if you take four 250GB drives and stripe them RAID 0, you’d have a 1TB Raid. In doing this, you spread out the information that is being written onto all the drives so that you get faster data transfers. This means that you can capture uncompressed video formats and play them back. The more drives you add, the faster the raid, the better the performance. RAID 1 is known as a protection RAID. You take 2 or more drives (need to be in pairs) and group them so that they again appear as one drive, but this time the information is MIRRORED.
Uses block-level striping with parity data distributed across all member disks. RAID 5 has achieved popularity due to its low cost of redundancy. Generally RAID 5 is implemented with hardware support for parity calculations. Every time a block is written to a disk in a RAID 5, a parity block is generated within the same stripe. A block is often composed of many consecutive sectors on a disk. A series of blocks (a block from each of the disks in an array) is collectively called a “stripe”. If another block, or some portion of a block, is written on that same stripe the parity block (or some portion of the parity block) is recalculated and rewritten. For small writes, this requires reading the old parity, reading the old data, writing the new parity, and writing the new data. The disk used for the parity block is staggered from one stripe to the next, hence the term “distributed parity blocks”.
