Click here to monitor SSC
SQLServerCentral is supported by Redgate
 
Log in  ::  Register  ::  Not logged in
 
 
 


RAID 5 Parity


RAID 5 Parity

Author
Message
Steve Jones
Steve Jones
SSC-Dedicated
SSC-Dedicated (36K reputation)SSC-Dedicated (36K reputation)SSC-Dedicated (36K reputation)SSC-Dedicated (36K reputation)SSC-Dedicated (36K reputation)SSC-Dedicated (36K reputation)SSC-Dedicated (36K reputation)SSC-Dedicated (36K reputation)

Group: Administrators
Points: 36008 Visits: 18728
Comments posted to this topic are about the item RAID 5 Parity

Follow me on Twitter: @way0utwest
Forum Etiquette: How to post data/code on a forum to get the best help
My Blog: www.voiceofthedba.com
happycat59
happycat59
Hall of Fame
Hall of Fame (3.6K reputation)Hall of Fame (3.6K reputation)Hall of Fame (3.6K reputation)Hall of Fame (3.6K reputation)Hall of Fame (3.6K reputation)Hall of Fame (3.6K reputation)Hall of Fame (3.6K reputation)Hall of Fame (3.6K reputation)

Group: General Forum Members
Points: 3562 Visits: 3097
Mmm, terminology is getting in my way for this one. My definition for parity (rightly or wrongly) applies at the byte level (Parity Bit).

For RAID 5, I have normally used the term "checksum" which is the value stored on 1 of the 3 disks required to store a single value,



Steve Jones
Steve Jones
SSC-Dedicated
SSC-Dedicated (36K reputation)SSC-Dedicated (36K reputation)SSC-Dedicated (36K reputation)SSC-Dedicated (36K reputation)SSC-Dedicated (36K reputation)SSC-Dedicated (36K reputation)SSC-Dedicated (36K reputation)SSC-Dedicated (36K reputation)

Group: Administrators
Points: 36008 Visits: 18728
A Better reference: http://technet.microsoft.com/en-us/library/cc938485.aspx

Checksum isn't a term I've seen associate with RAID. Almost always things are listed as parity calculations.

Follow me on Twitter: @way0utwest
Forum Etiquette: How to post data/code on a forum to get the best help
My Blog: www.voiceofthedba.com
Evil Kraig F
Evil Kraig F
SSCertifiable
SSCertifiable (5.7K reputation)SSCertifiable (5.7K reputation)SSCertifiable (5.7K reputation)SSCertifiable (5.7K reputation)SSCertifiable (5.7K reputation)SSCertifiable (5.7K reputation)SSCertifiable (5.7K reputation)SSCertifiable (5.7K reputation)

Group: General Forum Members
Points: 5695 Visits: 7660
Cat, it's for both, and same purpose. In a RAID 5, for each section of disk (I forget the break out) in say a 4 disk array, 3 have data, one has a parity to make sure the other three stay intact. Because of that parity, you can assume the data on the 'lost' disk while it's replaced, and rebuild it, due to reverse construction of the bit/bytes. Same concept, expanded further.

Lose two drives and it's game over though, as most folks are well aware. Smile


- Craig Farrell

Never stop learning, even if it hurts. Ego bruises are practically mandatory as you learn unless you've never risked enough to make a mistake.

For better assistance in answering your questions | Forum Netiquette
For index/tuning help, follow these directions. |Tally Tables

Twitter: @AnyWayDBA
SQLRNNR
SQLRNNR
SSC-Insane
SSC-Insane (21K reputation)SSC-Insane (21K reputation)SSC-Insane (21K reputation)SSC-Insane (21K reputation)SSC-Insane (21K reputation)SSC-Insane (21K reputation)SSC-Insane (21K reputation)SSC-Insane (21K reputation)

Group: General Forum Members
Points: 21067 Visits: 18258
Thanks for the question.

Here is another explanation that makes some sense.
http://riceball.com/d/content/raid-5-parity-what-it-and-how-does-it-work



Jason AKA CirqueDeSQLeil
I have given a name to my pain...
MCM SQL Server, MVP


SQL RNNR

Posting Performance Based Questions - Gail Shaw

UMG Developer
UMG Developer
SSCrazy
SSCrazy (2.3K reputation)SSCrazy (2.3K reputation)SSCrazy (2.3K reputation)SSCrazy (2.3K reputation)SSCrazy (2.3K reputation)SSCrazy (2.3K reputation)SSCrazy (2.3K reputation)SSCrazy (2.3K reputation)

Group: General Forum Members
Points: 2280 Visits: 2204
Thanks for the question Steve!
Stewart "Arturius" Campbell
Stewart "Arturius" Campbell
SSCertifiable
SSCertifiable (5.8K reputation)SSCertifiable (5.8K reputation)SSCertifiable (5.8K reputation)SSCertifiable (5.8K reputation)SSCertifiable (5.8K reputation)SSCertifiable (5.8K reputation)SSCertifiable (5.8K reputation)SSCertifiable (5.8K reputation)

Group: General Forum Members
Points: 5765 Visits: 7128
Thanks for the question.

____________________________________________
Space, the final frontier? not any more...
All limits henceforth are self-imposed.
“libera tute vulgaris ex”
Koen Verbeeck
Koen Verbeeck
SSCoach
SSCoach (16K reputation)SSCoach (16K reputation)SSCoach (16K reputation)SSCoach (16K reputation)SSCoach (16K reputation)SSCoach (16K reputation)SSCoach (16K reputation)SSCoach (16K reputation)

Group: General Forum Members
Points: 16380 Visits: 13199
Nice question, thanks.
Luckily I had the Wikipedia page for RAID bookmarked, in case new QotD featuring RAID would arrise :-)



How to post forum questions.
Need an answer? No, you need a question.
What’s the deal with Excel & SSIS?

Member of LinkedIn. My blog at SQLKover.

MCSA SQL Server 2012 - MCSE Business Intelligence
Duncan Pryde
Duncan Pryde
Hall of Fame
Hall of Fame (3.4K reputation)Hall of Fame (3.4K reputation)Hall of Fame (3.4K reputation)Hall of Fame (3.4K reputation)Hall of Fame (3.4K reputation)Hall of Fame (3.4K reputation)Hall of Fame (3.4K reputation)Hall of Fame (3.4K reputation)

Group: General Forum Members
Points: 3396 Visits: 1552
Thanks for the question. Reading the article, I now understand RAID 2, 3 and 4 as well.

But won't we all be using ZFS in a few years anyway? ;-)
happycat59
happycat59
Hall of Fame
Hall of Fame (3.6K reputation)Hall of Fame (3.6K reputation)Hall of Fame (3.6K reputation)Hall of Fame (3.6K reputation)Hall of Fame (3.6K reputation)Hall of Fame (3.6K reputation)Hall of Fame (3.6K reputation)Hall of Fame (3.6K reputation)

Group: General Forum Members
Points: 3562 Visits: 3097
Craig Farrell (3/24/2011)
Cat, it's for both, and same purpose. In a RAID 5, for each section of disk (I forget the break out) in say a 4 disk array, 3 have data, one has a parity to make sure the other three stay intact. Because of that parity, you can assume the data on the 'lost' disk while it's replaced, and rebuild it, due to reverse construction of the bit/bytes. Same concept, expanded further.

Lose two drives and it's game over though, as most folks are well aware. Smile


I believe that the data is actually stored on 3 disks...2 have the actual data and the 3rd has the exclusive OR of the other 2 disks. Using this, if you loose any one of the 3 disks that store the data you are after, the other 2 have enough information to give to retrieve the data. This basic pattern is used regardless of the number of disks in the array. When there are more than 3 disks, each chunk of data is still stored on 3 of the disks. The controller manages the allocation of disk space to ensure that all disks on the array are utilised.

Steve - whilst you may not have heard of checksum (Vs parity) in relation to RAID 5 , try searching google for "RAID 5 checksum". I do agree that you can view this as a "parity" but I am one of them dinosaurs who have been around since the days of punch cards, paper tape and magnetic tape. Parity back then was more to do with detecting error.



Go


Permissions

You can't post new topics.
You can't post topic replies.
You can't post new polls.
You can't post replies to polls.
You can't edit your own topics.
You can't delete your own topics.
You can't edit other topics.
You can't delete other topics.
You can't edit your own posts.
You can't edit other posts.
You can't delete your own posts.
You can't delete other posts.
You can't post events.
You can't edit your own events.
You can't edit other events.
You can't delete your own events.
You can't delete other events.
You can't send private messages.
You can't send emails.
You can read topics.
You can't vote in polls.
You can't upload attachments.
You can download attachments.
You can't post HTML code.
You can't edit HTML code.
You can't post IFCode.
You can't post JavaScript.
You can post emoticons.
You can't post or upload images.

Select a forum

































































































































































SQLServerCentral


Search