Storage Management Strategies for the CIO
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NEC Corp.'s RAID-TM or triple mirror (implemented in its D-Series systems) aims to solve RAID 1 data loss risk if both the primary and mirror drive fail or if there's a non-recoverable read error. RAID-TM writes data simultaneously to three separate HDDs so if two HDDs fail or there are unrecoverable read errors in the same mirror, the app still has access to its data with no degradation in performance even as the drives are rebuilt. The advantage is performance; the disadvantage is far less usable capacity.
RAID-X is an IBM XIV Storage System innovation that uses a wide stripe to reduce RAID tradeoffs of performance and data loss risk. It's basically a variation of RAID 10 that uses intelligent risk algorithms to randomly distribute block mirrors throughout the entire array. This approach allows XIV to reconstruct the data on very large 2 TB HDDs in less than 30 minutes. As with all mirroring technology, the tradeoff is reduced usable capacity.
Hewlett-Packard Co.'s LeftHand Networks and Pivot3 Inc. provide similar variations of Network RAID for their x86-based clustered iSCSI storage. Network RAID leverages the concept of RAID, but uses storage nodes as its lowest component level instead of disk drives. This allows it to distribute a logical volume's data blocks across the cluster with one to four data mirrors depending on the Network RAID level. Ongoing block-level, self-healing nodal health checks allow Network RAID to copy and repair the data to another
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node before a failure occurs. This decreases the probability of a hard disk drive fault or non-recoverable read error causing a performance-sapping rebuild; but like all mirroring technology, it reduces the amount of usable storage.
These are just some of the RAID + innovation technologies. Others are currently incubating, including proposals for RAID 7 (triple parity and more) or TSHOVER (triple parity).
RAID + transformation
There are also RAID alternatives that attempt to re-invent RAID. They typically use RAID and are layered on top of it in some way. The concept is to keep what's good about RAID and fix the rest. Examples of transformation technologies include self-healing storage and BeyondRAID.
This was first published in May 2010
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