How Striping With Parity (RAID-5) Works

RAID-5 provides data redundancy through the use of parity (a calculated value that the system uses to reconstruct data after a failure). While the data is written to a RAID-5 volume, parity is also calculated by perferming an exclusive OR (XOR) procedure on data. The resulting parity is then written to another part of the volume. If a portion of a RAID-5 volume fails, the data that was on that portion of the failed volume can be recreated from the remaining data and the partity.

RAID-5 offers data redundancy similar to mirroring, while requiring less disk space. RAID-5 read performance is similar to that of striping but with relatively slow write performance. RAID-5 is useful if the database workload is read-intesive (as in many data warehousing applications). You can snapshot a RAID-5 volume and move a RAID-5 subdisk without losing redundancy.

How Striping (RAID-0) Works
Striping is a technique of mapping data so that the data is interleaved among multiple physical disks. Data is allocated in equal-size units (called strip units) that are interleaved between the disks. Each stripe units is a set of contiguous blocks on a disk. A stripe consists of the set of stripe units at the same position across all columns. A column is a set of one or more subdisk within a striped plex.

Striping is useful if we need large amounts of data written to or read from physical disk, and performance is important. Striping is also helpful in balancing the I/O laod from multi-user applications across multiple disks. By using parallel data transfer to and from multiple disks, striping significantly improves data-access performance.

When striping across multiple disks, failure of any one disk will make the entire volume unusable.

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