Feature

Alternatives to RAID

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The various forms of RAID have been around for a long time and have done a good job of protecting data. But high-capacity drives and new performance demands have spurred development of RAID alternatives.

Redundant array of independent disks (RAID) has been the standard for disk-based data protection since 1989, and is a proven and reliable method that's considered a basic data storage building block. Basic storage principles tend to change very slowly and, despite its popularity and track record, change is coming to RAID.

To gain more insight into why an alternative to RAID might be appealing requires some understanding about RAID and the growing problems with the technology.

RAID shortcomings in the 21st century

The purpose of RAID is to protect data in the event a hard disk drive (HDD) fails. When that failure occurs, data from that failed HDD (or multiple HDDs) is recreated from parity or copied from a mirror, depending on the type of RAID in use. Disk drives are electro-mechanical devices that have the highest probability of a failure and the lowest mean time between failures (MTBF) in any storage system.

It takes a lot of HDDs to keep up with the rapid growth rate of data storage that analyst firms like IDC, Gartner and Enterprise Strategy Group peg at somewhere between 50% and 62% per year. Statistically speaking, more hard disk drives mean more HDD failures. Disk drive manufacturers have continually increased

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HDD density, and today we have 2 TB SATA and are likely going to 4 TB by the end of this year. Even high-performance SAS and Fibre Channel (FC) drive capacities are pushing 600 GB. RAID problems quickly become evident when a rebuild is required with those increasingly dense drives.

Each RAID type (see "Traditional RAID levels," below) has tradeoffs in write performance, read performance, level of data protection, speed of data rebuilds and the usable storage on each hard disk drive. For example, if guaranteeing data availability is the top priority, then some variation of mirroring or multiple mirrors (RAID 1, 10, triple mirror, etc.) will be required. Having full copies of the data on other HDDs or RAID sets simplifies protection and recovery of the data but at a severe and tangible cost because each mirror reduces usable storage by the same amount of the original data. In addition, system resources are required for every copy, which can impair I/O performance. Realistically, most organizations aren't this overprotective; most use RAID 5 and/or RAID 6.

Click here to get a PDF of the Traditional RAID Levels chart.

This was first published in May 2010

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