Click here to monitor SSC
SQLServerCentral is supported by Red Gate Software Ltd.
 
Log in  ::  Register  ::  Not logged in
 
 
 
        
Home       Members    Calendar    Who's On


Add to briefcase 12345»»»

RAID 1 vs. RAID 10 Expand / Collapse
Author
Message
Posted Tuesday, December 23, 2008 12:43 PM


Old Hand

Old HandOld HandOld HandOld HandOld HandOld HandOld HandOld Hand

Group: General Forum Members
Last Login: Today @ 12:18 PM
Points: 362, Visits: 885
Lots of great articles on the intertubez about disk alignment and RAID configurations but I haven't found an answer (or a good way to test, and yes I know about SQLIO) for a simple scenario:

Suppose I have 4 local physical disks available to me and I'm going to create an OLTP DB (for the sake of arguing let's say we're 50\50 on reads and writes, or otherwise average usage). Here are two scenarios that I would consider:

1) Two RAID 1 drives. Create the DB with two data files, i.e. one data file on each drive
2) One RAID 10 drive. Create the DB with one single data file

In the RAID 1 scenario (as I understand it) SQL will round robin writes between the two data files, thus creating a software equivalent of striping. RAID 10, on the other hand, handles the striping at a hardware level. Those differences aside, I haven't found a good technical explanation - or numbers to back it - for what's happening under the covers that would make me believe one option is better than the other.

So which of these two scenarios is more ideal and why?


Kendal Van Dyke
http://kendalvandyke.blogspot.com/
Post #624961
Posted Tuesday, December 23, 2008 1:06 PM


SSC-Dedicated

SSC-DedicatedSSC-DedicatedSSC-DedicatedSSC-DedicatedSSC-DedicatedSSC-DedicatedSSC-DedicatedSSC-DedicatedSSC-DedicatedSSC-DedicatedSSC-DedicatedSSC-DedicatedSSC-Dedicated

Group: Administrators
Last Login: Today @ 4:56 PM
Points: 31,168, Visits: 15,612
I would argue Raid 10 for one reason. You're not 100% sure of the usage and balance among the drives and with 2 R1s, you can run out of space on one, have space on the other. With one large R10, it gets handled and you get to use all the space.

Other than that, I'm not sure there's a great technical argument for R1 v R10.







Follow me on Twitter: @way0utwest

Forum Etiquette: How to post data/code on a forum to get the best help
Post #624975
Posted Tuesday, December 23, 2008 2:13 PM


SSCrazy Eights

SSCrazy EightsSSCrazy EightsSSCrazy EightsSSCrazy EightsSSCrazy EightsSSCrazy EightsSSCrazy EightsSSCrazy EightsSSCrazy EightsSSCrazy Eights

Group: General Forum Members
Last Login: Wednesday, October 15, 2014 9:14 AM
Points: 9,294, Visits: 9,483
You should worry about your Log file before you add a second data file.

-- RBarryYoung, (302)375-0451 blog: MovingSQL.com, Twitter: @RBarryYoung
Proactive Performance Solutions, Inc.
"Performance is our middle name."
Post #625034
Posted Tuesday, December 23, 2008 2:19 PM


Old Hand

Old HandOld HandOld HandOld HandOld HandOld HandOld HandOld Hand

Group: General Forum Members
Last Login: Today @ 12:18 PM
Points: 362, Visits: 885
RBarryYoung (12/23/2008)
You should worry about your Log file before you add a second data file.


Ummm....thanks....but kinda not the point of the post. I'm looking for technical reasons why a single data file on RAID 10 is better than two data files on two RAID 1's.

But FWIW I'll stick my log files on a different drive than my data files altogether.


Kendal Van Dyke
http://kendalvandyke.blogspot.com/
Post #625040
Posted Tuesday, December 23, 2008 9:52 PM
Right there with Babe

Right there with BabeRight there with BabeRight there with BabeRight there with BabeRight there with BabeRight there with BabeRight there with BabeRight there with Babe

Group: General Forum Members
Last Login: 2 days ago @ 9:34 AM
Points: 754, Visits: 3,164
I doubt that there is much difference from a performance standpoint ... the raid 1 scenario would presumably require a tiny increase in system resources. Raid 10 would appear to be a little easier to manage in as much as you would be dealing with one file rather than two. If I remember correctly, fragmentation statistics aren't accurate for multiple files either.

The above all assumes that the 2 files are across one filegroup (as that would use the proportional fill algorithm) - if one were to split the database into two filegroups (one file per filegroup) then there are other potential advantages from the raid 1 scenario .... filegroup backups, partitioning etc etc.

Post #625162
Posted Wednesday, December 24, 2008 2:19 AM
SSCrazy

SSCrazySSCrazySSCrazySSCrazySSCrazySSCrazySSCrazySSCrazy

Group: General Forum Members
Last Login: Today @ 10:18 AM
Points: 2,667, Visits: 5,880
Another possible implication of two raid 1s would be if they were the same filegroup, with a massive table that was frequently being scanned. If I remember rightly in that situation (table scan, table on more than 1 file group) SQL Server will initiate multiple threads (one per file) and run the scans in parallel.

Mike



Post #625240
Posted Wednesday, December 24, 2008 8:19 AM


SSCrazy Eights

SSCrazy EightsSSCrazy EightsSSCrazy EightsSSCrazy EightsSSCrazy EightsSSCrazy EightsSSCrazy EightsSSCrazy EightsSSCrazy EightsSSCrazy Eights

Group: General Forum Members
Last Login: Wednesday, October 15, 2014 9:14 AM
Points: 9,294, Visits: 9,483
kendal.vandyke (12/23/2008)
I'm looking for technical reasons why a single data file on RAID 10 is better than two data files on two RAID 1's.

Ah, I see, I misunderstood the intent of your question. Sorry...


-- RBarryYoung, (302)375-0451 blog: MovingSQL.com, Twitter: @RBarryYoung
Proactive Performance Solutions, Inc.
"Performance is our middle name."
Post #625408
Posted Wednesday, December 24, 2008 8:30 AM


Old Hand

Old HandOld HandOld HandOld HandOld HandOld HandOld HandOld Hand

Group: General Forum Members
Last Login: Today @ 12:18 PM
Points: 362, Visits: 885
Ah, I see, I misunderstood the intent of your question. Sorry...


No apologies necessary! :)


Kendal Van Dyke
http://kendalvandyke.blogspot.com/
Post #625417
Posted Wednesday, December 24, 2008 12:49 PM


SSCertifiable

SSCertifiableSSCertifiableSSCertifiableSSCertifiableSSCertifiableSSCertifiableSSCertifiableSSCertifiableSSCertifiable

Group: General Forum Members
Last Login: Today @ 2:09 PM
Points: 6,465, Visits: 13,918
i would say the RAID 10 array is best as it offers the best performance and fault tolerance combined into one package. The downside of RAID 10 is the disk cost (no of disks required)

-----------------------------------------------------------------------------------------------------------

"Ya can't make an omelette without breaking just a few eggs"
Post #625549
Posted Wednesday, December 24, 2008 3:37 PM


Old Hand

Old HandOld HandOld HandOld HandOld HandOld HandOld HandOld Hand

Group: General Forum Members
Last Login: Today @ 12:18 PM
Points: 362, Visits: 885
i would say the RAID 10 array is best as it offers the best performance and fault tolerance combined into one package. The downside of RAID 10 is the disk cost (no of disks required)


Maybe the question was misunderstood. I proposed two scenarios for how to configure 4 disks to hold data. A single RAID 10 with 4 disks is just as fault tolerant as two RAID 1 drives - each can lose 1 disk per pair. Likewise the disk cost is the same in the question I asked.

As for performance, I'm looking for something solid to show that RAID 10 would be better than RAID 1 or vice versa. I was really hoping someone knew enough about what's going on under the covers (e.g. IO paths, threads, etc.) to make it clear.


Kendal Van Dyke
http://kendalvandyke.blogspot.com/
Post #625589
« Prev Topic | Next Topic »

Add to briefcase 12345»»»

Permissions Expand / Collapse