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Tag: RAID

RAID (redundant array of independent disks, originally redundant array of inexpensive disks) is a storage technology that combines multiple disk drive components into a logical unit. Data is distributed across the drives in one of several ways called “RAID levels”, depending on what level of redundancy and performance (via parallel communication) is required. In October 1986, the IBM S/38 announced “checksum”. Checksum was an implementation of RAID-5. The implementation was in the operating system and was software only and had a minimum of 10% overhead. The S/38 “scatter loaded” all data for performance. The downside was the loss of any single disk required a total system restore for all disks. Under checksum, when a disk failed, the system halted and was then shutdown. Under maintenance, the bad disk was replaced and then a parity-bit disk recovery was run. The system was restarted using a recovery procedure similar to the one run after a power failure. While difficult, the recovery…