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#153560 - 2005-12-16 08:18 PM RAID Question...
jdogg Offline
Getting the hang of it

Registered: 2003-09-11
Posts: 91
Loc: RTP, North Cakalaka, USA
Hey guys...
I wanted to post a techie question for fellow server geeks.
I am designing a Active Directory infrastructure and I am requesting a certain RAID design based on Microsoft Best Practices.

My question is:
Even if two separate arrays (RAID 1) are on the same controller on the same channel, doesn't performance improve if one array is doing mostly write operations and the other doing mostly read operations?

Just wondering... perhaps you can find a reputable article that can back up my argument?

Not a big deal, I think the guy that is disputing me is just trying to prove that his "member" is larger than mine. While that may be the case, it is possible (and likely) that his is as insignificant as my own. LOL Did I say that out loud? hehe...

-Jdogg

P.S. - Here is an excerpt from the Microsoft document that details requirements for the 2003 AD disk recommendations:
Code:

Operating system files          Read and write operations	RAID 1
Active Directory log files	Mostly write operations	        RAID 1
AD database & SYSVOL share	Mostly read operations	        RAID 1 or RAID 0+1
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#153561 - 2005-12-16 08:35 PM Re: RAID Question...
NTDOC Administrator Offline
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Registered: 2000-07-28
Posts: 11628
Loc: CA
Quote:

doesn't performance improve if one array is doing mostly write operations and the other doing mostly read operations



I don't see a real comparison to something else in that question.

There are a lot of factors to take into account when determining performance.

The more spindles the better performance in general. Having on separate controllers is better too.

This only scratches the surface though of performance measurements.
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#153562 - 2005-12-16 09:26 PM Re: RAID Question...
StarwarsKid Offline
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Registered: 2005-06-15
Posts: 506
Loc: Oregon, USA
You may want to see if this depth of analysis is even needed. How many users will this DC support? How many secondary DCs will there be? Will they be single function or multi-function servers?

With the hardware muscle power newer servers are being shipped with, all this subdivision of AD functions becomes a moot point, (depending on your size).

Remember, Microsoft wants the multi-national company market. They're training techs to SuperSize all design plans in hopes that people start actually using their product in mega-corporations. That's their main reason for being so "nth degree" on their server recommendations for their products.
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and let the discerning get guidance- Proverbs 1:5

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#153563 - 2005-12-19 03:02 PM Re: RAID Question...
Richard H. Administrator Offline
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Registered: 2000-01-24
Posts: 4946
Loc: Leatherhead, Surrey, UK
Quote:

My question is:
Even if two separate arrays (RAID 1) are on the same controller on the same channel, doesn't performance improve if one array is doing mostly write operations and the other doing mostly read operations?



I'm not sure you've framed your question fully.

When you say "improve" what is is that you are comparing it against? What is the less efficient option that you are thinking of?

Your constraints will be the amount of disk cache memory on the disks and controller card, how it is used and how quickly disk blocks are written (and read). It is unlikely that your controller itself will be an IO bottle-neck unless you have a lot of spindles in which case I guess SCSI arbitration will begin to have an impact.
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#153564 - 2005-12-19 08:53 PM Re: RAID Question...
jdogg Offline
Getting the hang of it

Registered: 2003-09-11
Posts: 91
Loc: RTP, North Cakalaka, USA
Yes, I agree I need to re-phrase.

Currently our OS/Hardware team built the Domain Controller with the following config:
OS - RAID 1 Array, Controller 1, Channel 1
Everything else - RAID 5 Array, Controller 1, Channel 1
----------------
We requested that he remove the RAID 5 Array and rebuild with the Microsoft Best Practice (Three RAID 1's, detailed above).
However, he contended that we would gain nothing from this, due to the fact that the arrays would be on the same channel on the same controller.

I contended that the performance with three RAID 1's would be better than one RAID 1 (OS) and one RAID 5 (everything else) due to the fact that the log files and the database each needed their own array because of the differing read/write operation concentrations.

All else being equal, who is right?
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#153565 - 2005-12-19 09:07 PM Re: RAID Question...
Mart Moderator Offline
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Registered: 2002-03-27
Posts: 4673
Loc: The Netherlands
MS best practice, hmmm....
Been doing it like this for several years now and never lost any critical data or speed. Ran several SAP R/3 servers like this and had no performance problems caused by data storage. Memory and CPU load is a different story but that's not the issue here.

Code:

Array 1 RAID1 with only two disks.
	C:\ - OS and apps installation source.
	D:\ - Page file.

Array 2 RAID5 with at least 3 disks.
	E:\ - DB's like Exchange, SQL, file storage or whatever is needed.
	F:\ - Depends on the use of the server. If it's a SQL server I always put the SQL Transaction logs here. Not all of my servers have a F:\ disk, depends on the use of the server.


On the matter of performance. Also depending on the use of the server in my cases it has proven to me that putting the array’s on separate channels will be (somewhat) faster. If it's all on one channel everything that want's to read or write from or to the HDD's will have to wait until the channel is free. Multiple channels can be accessed simultaneously so multiple channels will be faster. Just from experience, no science behind this.

Edited by Mart (2005-12-19 09:09 PM)
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#153566 - 2005-12-19 09:19 PM Re: RAID Question...
jdogg Offline
Getting the hang of it

Registered: 2003-09-11
Posts: 91
Loc: RTP, North Cakalaka, USA
Yes, I agree that multiple channels/controllers would help.
However, that isn't available in this case.

Really I think the argument is based on personal bragging rights.
The guy I am contending with loves to bring up issues, and I just wanted to get another opinion in regards to our situation.

I suppose the performance benefit or lack of it would be minimal given our scenario, but like I said this is more of a bragging rights thing.
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#153567 - 2005-12-19 09:56 PM Re: RAID Question...
NTDOC Administrator Offline
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Registered: 2000-07-28
Posts: 11628
Loc: CA
In a small data set the RAID 1 would be faster. In a larger data set the READ operations would be faster on RAID5 as there are more drive spindles to pull pieces of the data from.

There is more overhead as well, but in your case with such a small dataset the RAID1 would be faster.
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#153568 - 2005-12-20 12:13 AM Re: RAID Question...
Les Offline
KiX Master
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Registered: 2001-06-11
Posts: 12734
Loc: fortfrances.on.ca
Yes, RAID5 stripes across multiple drives including the parity. The reduced redundancy writes would reduce the overhead as well.

I will at times go with a RAID1/RAID5 split (2 + 4) backplane and two channels for SQL servers.
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#153569 - 2005-12-20 03:45 AM Re: RAID Question...
Sealeopard Offline
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Registered: 2001-04-25
Posts: 11165
Loc: Boston, MA, USA
RAID5 get spenalized slightly for writes. For the real deal on RAID see e.g. http://www.storagereview.com/guide2000/ref/hdd/perf/raid/index.html

For SQL on local drives I'd go for RAID1 OS, RAID 0+1 LOG and RAID5 DB for a transactional system. For a data warehosue system, I'd put the logs on RAIFD1 and the DB on RAID0+1 and a lot of spindles. But then agian, most of our stuff ison a sAN anyway, thus RAID doesn't matter much anymore at that point as it's abstracted.
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#153570 - 2005-12-20 07:57 PM Re: RAID Question...
jdogg Offline
Getting the hang of it

Registered: 2003-09-11
Posts: 91
Loc: RTP, North Cakalaka, USA
Thanks for all the discussion guys.
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