Parity computations are used in RAID drive arrays for fault tolerance by calculating the data in two drives and storing the results on a third. The parity is computed by XOR'ing a bit from drive 1 with a bit from drive 2 and storing the result on drive 3 (to learn about XOR, see OR). After a failed drive is replaced, the RAID controller rebuilds the lost data from the other two drives. RAID systems often have a "hot" spare drive ready and waiting to replace a drive that fails. See RAID.
 | Reproduced with permission from Computer Desktop Encyclopedia. Copyright (c) 1981-2009 The Computer Language Company Inc. All rights reserved. |
Additional Resources
- RAIDfail: Don't use RAID 5 on small arrays
- RAIDfail: Don't use RAID 5 on small arraysDroboSo.. the article says not use use RAID 5 - then recommends that the consumer buys a box Drobo - which essentially just operates as a RAID 5 array when its full???? (put in 4 x 1 TB disks and get 3...
- Discussion threads 2009-05-19
- RAIDfail: Don't use RAID 5 on small arrays
- Big storage companies stopped recommending RAID 5 a couple of years ago. But I still see small 4-drive arrays touting RAID 5 for home and small office use. Big mistake. You want to save money, but you also want to keep your data. RAID 5 isn't...
- Blog posts 2009-05-19
- Better than RAID: the new DroboPro
- RAID is a bad idea for home users since its management complexity and failure modes create more problems than it solves. But protection from 1 - or better yet 2 - drive failures is a very GOOD idea. Data protection for the rest of us ...
- Blog posts 2009-04-09
- New DroboPro NAS has 8 drive bays for 16TB storage
- New DroboPro NAS has 8 drive bays for 16TB storageDrobo Pro, will change the landscape of reliable storageSmart move Data Robotics, make a great idea behind Drobo even better with Drobo Pro. This approach will serve well for the transition from tape back up strategies to hard disks. ...
- Discussion threads 2009-04-07
- Anyone here own a 1.5TB Seagate Barracuda 7200.11?
- Anyone here own a 1.5TB Seagate Barracuda 7200.11?ConfusedSeaTools Enterprise Edition only scans for SCSI only found my DVD burner, but my 1.5TB is a SATA drive.Anyway, my drive has firmware version SD17 according to "SeaTools for Windows". I cannot find any information regarding part number, though.I haven't experienced any appreciable...
- Discussion threads 2008-11-11
- LaCie's 5big Network offers five drive bays, up to 7.5TB storage
- LaCie is bringing its distinctive aesthetic sense to small business networked storage with its new 5big Network device, which offers—surprise—five drive bays and up to a whopping 7.5 terabytes of capacity. If that's still not sufficient (or you want to back up what's on the 5big Network), the included USB...
- Blog posts 2008-10-13
- Your capacity will vary
- Your capacity will varyA "wordo"I dictated the first draft of the article, and while the software is pretty good about not misspelling words, if it gets the wrong word it can be hard to spot. Like "desk" for "disk". Thanks for noting it.Robinhours of ten?Should it be "powers of ten"?If...
- Discussion threads 2008-09-17
- Your capacity will vary
- By an increasing amount Why is your storage capacity always less, sometimes a lot less, then what you see advertised on the box? There is only one rule: you will never get the capacity the vendor advertises. Storage vendors don't mean to be lying. They just...
- Blog posts 2008-09-16
- Thecus N3200
- The Thecus N3200 is an empty, three-bay NAS drive that sells for approximately $330. Though it doesn't provide any storage out of the box, it's still reasonably priced for a device that supports RAID and up to 3TB of storage. The device boasts a useful set of features, including printer...
- Product reviews 2008-09-09
- Maybe I was wrong about Mac Servers
- Maybe I was wrong about Mac ServersSo ZFS is the sole criteria for a quality server OS or not?Has data loss due the underlying file system really been the problem Robin and you are making it out to be?RE: Maybe I was wrong about Mac Serversye: Veritas VxFS indeed has...
- Discussion threads 2008-06-20
- Build your own Google
- In an earlier post I talked a bit about a start-up called Kickfire who are releasing an accelerated database appliance for MySQL applications in the 1TB-3TB range that gives comparable performance to an equivalent Oracle RDBMS setup for around a quarter of the price. Kickfire sounds compelling for utility...
- Blog posts 2008-06-05
- A New Minimum Density RAID-6 Code With a Word Size of Eight
- RAID-6 storage systems protect k disks of data with two parity disks so that the system of k + 2 disks may tolerate the failure of any two disks. Coding techniques for RAID-6 systems are varied, but an important class of techniques are those with minimum density, with an optimal...
- White papers 2008-04-01
- Leopard's Time Machine: Consider the 'bad and ugly' side of storage
- Before tackling my Thanksgiving Day's supper (which came at my nephew's apartment in the form of a steak this year instead of a turkey), I read through an article in the November ACM Queue about potential data reliability issues with high-capacity hard disks. The concerns over these new HDDs â€"...
- Blog posts 2007-11-23
- Data corruption is worse than you know
- Data corruption is worse than you knowOpportunity for software designers, maybe ...Maybe this is an opportunity for software designers to create and implement data integrity applications similar to the rise of security applications that are all the rage today. By and large, most software today does not have any data...
- Discussion threads 2007-09-18
- Is AMD's 65nm SOI process broken?
- Is AMD's 65nm SOI process broken?As soon as I read the headline...I knew it had to be George.Your bashing has become boring.Seems to be..and after all the SOI hubbub, too!Good topic. AMD made a huge stink about it's incredible and innovative SOI process a few years ago. That along...
- Discussion threads 2007-08-21
- 50 ways to lose your data
- Apologies to Paul SimonDisk drives are marvelous devices. Especially when they go "clunk" and stop working. I'm not kidding: at least you know your data is hosed. I prefer that to the silent data corruption you don't find out about until you can't access a file or your OS starts...
- Blog posts 2007-08-07
- Sorry about your broken RAID 5
- You didn't know?I'm sorry I was the one to tell you that RAID 5 is broken today and will be well and truly broken in 2009 (see Why RAID 5 stops working in 2009), but somebody had to do it. The good news is that the industry is ahead of...
- Blog posts 2007-07-24
- Review of Data Robotics' Drobo 'storage robot'
- Last week I gave a fairly harsh review of the Drobo "storage robot" product based on some initial investigation I did. I concluded that while it's possible to do some level of hard drive mixing, it really wasn't worth it since you didn't get meaningful capacity out of it. I...
- Blog posts 2007-05-30
- Why home RAID won't fly
- Why home RAID won't flyRight onA home server is a silly concept. Just backup your stuff easily and cheaply on an external hard disk in a USB casing. 500 GB storage for about $ 150.To top it off: this is a much "greener" solution as well... You only have to...
- Discussion threads 2007-05-29
- Why dumb-downed no-RAID storage is bad for consumers
- Data storage is a rapidly expanding area of consumer electronics because people have growing amounts of data at home along with the fact that they have more than one computer and devices that need to access the same data. Why should consumers have to choose between losing Desperate House Wives...
- Blog posts 2007-05-29
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