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Diagram of a RAID 1 setup. RAID 1 consists of an exact copy (or mirror) of a set of data on two or more disks; a classic RAID 1 mirrored pair contains two disks.This configuration offers no parity, striping, or spanning of disk space across multiple disks, since the data is mirrored on all disks belonging to the array, and the array can only be as big as the smallest member disk.
RAID (/ r eɪ d /; redundant array of inexpensive disks or redundant array of independent disks) [1] [2] is a data storage virtualization technology that combines multiple physical data storage components into one or more logical units for the purposes of data redundancy, performance improvement, or both.
RAID 5E, RAID 5EE, and RAID 6E (with the added E standing for Enhanced) generally refer to variants of RAID 5 or 6 with an integrated hot-spare drive, where the spare drive is an active part of the block rotation scheme. This spreads I/O across all drives, including the spare, thus reducing the load on each drive, increasing performance.
RAID 01, also called RAID 0+1, is a RAID level using a mirror of stripes, achieving both replication and sharing of data between disks. [3] The usable capacity of a RAID 01 array is the same as in a RAID 1 array made of the same drives, in which one half of the drives is used to mirror the other half.
While hardware RAID controllers have been available for a long time, they initially required expensive Parallel SCSI hard drives and aimed at the server and high-end computing market. SCSI technology advantages include allowing up to 15 devices on one bus, independent data transfers, hot-swapping , much higher MTBF .
Linux supports Matrix RAID and Rapid Storage Technology (RST) through device mapper, with dmraid tool, for RAID 0, 1 and 10. And Linux MD RAID, with mdadm tool, for RAID 0, 1, 10, and 5. Set up of the RAID volumes must be done by using the ROM option in the Matrix Storage Manager, then further configuration can be done in DM-RAID or MD-RAID. [10]
A flawed RAID 5/6 also exists, but can result in data loss.) [10] For RAID 1, the devices must have complementary sizes. For example, a filesystem spanning two 500 GB devices and one 1 TB device could provide RAID1 for all data, while a filesystem spanning a 1 TB device and a single 500 GB device could only provide RAID1 for 500 GB of data.
The RAID controller will notice that the storage elements are not in sync, will place the array in degraded mode, and – generally – will start a background resync (rebuild) operation. Simple mirroring solutions will resynchronize the entire array, block by block, across both drives, which can be quite time-consuming; this time can be ...