Home > Ask the Storage Technology Experts > Questions & Answers > In RAID 5, can parity information be exceeded?
Ask The Storage Expert: Questions & Answers
EMAIL THIS

In RAID 5, can parity information be exceeded?

Bruce Backa EXPERT RESPONSE FROM: Bruce Backa

Pose a Question
Other Storage Categories
Meet all Storage Experts
Become an Expert for this site
>
QUESTION POSED ON: 13 March 2003
I understand that RAID-5 has a limitation of 32 disks, but what puzzles me is with 3.1 terabytes of information stored on 31 100 GB drives. What happens if the parity information exceeds 100 GB?

>

The RAID algorithm doesn't allow for such a possibility. Each of the disks in your RAID is formatted into a fixed number of blocks of equal size. The data is then striped across these blocks, with the final block being used for a checksum. This means that any collection N-1 blocks can be used to reproduce all of the original data.

The system doesn't care what this data is -- user data or file system meta data. Any collection of N-1 blocks can be used to derive all the information. If the block onto which the data was written is still live, the data is simply read from there. If the disk that holds the block you need is down, then that block is calculated using the parity bits.

In a 32-drive array, each stripe would have 31 data blocks and 1 checksum block. The secret of success is that each drive uniquely holds one and only one block.


Digg This!    StumbleUpon Toolbar StumbleUpon    Bookmark with Delicious Del.icio.us   



RELATED RESOURCES
2020software.com, trial software downloads for accounting software, ERP software, CRM software and business software systems
Search Bitpipe.com for the latest white papers and business webcasts
Whatis.com, the online computer dictionary



Search and Browse the Expert Answer Center
Search and browse more than 25,000 question and answer pairs from more than 250 TechTarget industry experts.
Browse our Expert Advice



Search for Data Management Tools
TechTarget Storage Media
Storage Magazine View this month\\'s issue and subscribe today.
Storage Decisions Apply online for free conference admission.
SearchStorage.com
HomeNewsMagazineTopicsLearningMultimediaWhite PapersBlogsEventsAbout Us

About Us  |  Contact Us  |  For Advertisers  |  For Business Partners  |  Site Index  |  RSS
TechTarget provides technology professionals with the information they need to perform their jobs - from developing strategy, to making cost-effective purchase decisions and managing their organizations' technology projects - with its network of technology-specific websites, events and online magazines.

TechTarget Corporate Web Site  |  Media Kits  |  Site Map




All Rights Reserved, Copyright 2000 - 2009, TechTarget | Read our Privacy Policy
  TechTarget - The IT Media ROI Experts