Quorum and MSDTC in Clusters

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Quorum and MSDTC in Clusters

huskerwendy

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May 2, 2006 at 1:54 pm

#113089

We are going to be implementing a cluster using Windows Server 2003 EE and SQL Server 2005 EE. In my research, I've read that the Quorum drive should be at least 500 MB and should be installed on it's own drive. We will not have any drives that small in our RAID array. What is the average size of the quorum drive and how much I/O activity does it average?
Also, I've read that MSDTC needs at least 500 MB and it's own drive and not to put it on the same drive as the disk containing the Quorum. I just saw a post on this site that said they weren't using MSDTC. I thought you had to have MSDTC. Is that correct? How much I/O activity does MSDTC have? Can the Quorum and MSDTC reside on the same drive?
I appreciate your help!
Wendy

Wendy Schuman

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K. Brian Kelley SSC Guru Points: 114562 More actions · Answer 1

Our quorum drives aren't that small. They're basically 36 to 72 GB, whatever the smallest physical HD is for the array. We RAID 1 mirror those. The same is true of our DTC drives. In both cases the 500 MB is a minimum size, but if you're going to use physical drives, obviously your quorum and MSDTC drive sizes are going to be significantly larger.

You need MS DTC if you're going to do any sort of distributed transactions (linked servers, etc.) I don't remember if you have to have MS DTC, but we always configure it. If you're not using distributed transactions its existance from that perspective isn't necessary, but I don't remember if the setup will balk if MS DTC isn't configured. I know it's configuration steps are in the Microsoft KB articles for setting up a SQL Server cluster.

As far as your last question, according to Microsoft, MS DTC and the Quorum should not be on the same drive. The quorum drive is essential to your cluster and it's where the cluster configuration is stored. Therefore, you want no other processes potentially conflicting with respect to I/O. Hence the reason the recommendation is for Quorum to be on it's own set of physical drives. MS DTC can be very, very intensive on writes. Hence the reason for the change from Windows 2000 to Windows 2003. In Windows 2000 you ran comclust.exe on all nodes and that put DTC in the main cluster group, meaning it used the quorum drive. We noticed the difference in configuration recommendations and asked that question of MS, and that was their response: DTC could potentially conflict with the quorum (or even SQL Server), so put it on its own set of drives.

K. Brian Kelley
@kbriankelley

huskerwendy Hall of Fame Points: 3633 More actions · Answer 2

Thanks for the response, Brian! You answered all my questions.

Wendy

Wendy Schuman

huskerwendy Hall of Fame Points: 3633 More actions · Answer 3

I forgot to mention that we are planning to use a SAN with RAID DP. Does that make a difference as to where we would place the Quorum and MSDTC?

Thanks Again!

Wendy Schuman

K. Brian Kelley SSC Guru Points: 114562 More actions · Answer 4

They should at least be on separate logical drives. You'll probably want to get with your storage architect/administrator to determine the best way to allocate space on your given SAN. This might require a quick consult with your storage vendor. However, the optimal solution, at least from an MS perspective, is to have dedicated physical drives to both quorum and MS DTC.

K. Brian Kelley
@kbriankelley

Dexter Plaras Ten Centuries Points: 1000 More actions · Answer 5

Setup will not balk if you don't configure MS DTC. Actually you don't have to configure MS DTC if you don't do distributed transactions. That will probably saves you disk space since you don't have to provide one for MS DTC.