raid 0 vs. raid1

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• RAID 0 (block-level striping without parity or mirroring) provides improved performance and additional storage but no redundancy or fault tolerance (making it not true RAID, according to the acronym's definition). However, because of the similarities to RAID (especially the need for a controller to distribute data across multiple disks), simple stripe sets are normally referred to as RAID 0. Any disk failure destroys the array, and the likelihood of failure increases with more disks in the array (at a minimum, catastrophic data loss is twice as likely compared to single drives without RAID). A single disk failure destroys the entire array because when data is written to a RAID 0 volume, the data is broken into fragments called blocks. The number of blocks is dictated by the stripe size, which is a configuration parameter of the array. The blocks are written to their respective disks simultaneously on the same sector. This allows smaller sections of the entire chunk of data to be read off the drive in parallel, increasing bandwidth. RAID 0 does not implement error checking, so any error is uncorrectable. More disks in the array means higher bandwidth, but greater risk of data loss.
• In RAID 1 (mirroring without parity or striping), data is written identically to multiple disks (a "mirrored set"). Although many implementations create sets of 2 disks, sets may contain 3 or more disks. Array provides fault tolerance from disk errors or failures and continues to operate as long as at least one drive in the mirrored set is functioning. With appropriate operating system support, there can be increase to read performance, and only a minimal write performance reduction. Using RAID 1 with a separate controller for each disk is sometimes called duplexing.

raid 1+0：既有mirror又能strip，所以performance和fault tolerance都很好。