SQL Server Performance Forum – Threads Archive

SAN versus DAS

We have a contractor that is hired to design a SQL Server cluster for a core system and he is pushing for the user database transaction log and tempdb to be on a DAS (direct attached storage) and the rest to be on the SAN, he is saying for performance reason(DAS will be faster then SAN and so the database performance will be better). I couldn’t find any "official" performance comparison between DAS and SAN but for one I know that we will have 2 points of failure instead of one.
I will really appreciate your thoughts regarding this topic.

What do you mean by "official"?
Check this
http://whitepapers.zdnet.co.uk/0,39025945,60041033p,00.htm
You will some information

That’s like saying a blue car is faster than a red car. If you configure your SAN correctly you can get great performance. Unfortunally most people configuring SAN have no idea about how to set them up for optimal database performance and configure it the same as file server usage and such. So many DBA’s have bad experiences with SANs becasue of this. If you suspect you have these kind of people in your organisation then you could take the safe road and use DAS (this still has to be configured correctly). If you have people who know how to set up, configure and test the SAN for database usage you can use a SAN.

I would be wary of using NAS for the tempdb and log files. How is he wanting to configure this? MeanOldDBA
[email protected] When life gives you a lemon, fire the DBA.

He just want to have them on DAS, his assumtion is that because DAS is a direct link the writing to the logs and tempdb would be faster then on SAN, so the database will perform better.

What will make you wary?

The speed associated with either selection can vary based on configuration (stripe size, RAID levels, etc). To say that the DAS is going to perform better just because it is connected through a internal controller is not a good reason for me. If you have SAN storage in house already and it is high-end storage you will most likely get better performance out of that and you get much higher availability. If you have a low end SAN installation then he may be correct. Too hard to come up with anything concrete unless you provide some details on both the SAN configuration and the DAS configuration. David

Actually, I am still in third grade and don’t read very well sometimes. [<img src=’/community/emoticons/emotion-1.gif’ alt=’

‘ />] I thought you said NAS instead of DAS. DAS might be a good idea for tempdb and the log files IF it’s configured appropriately. If you can provide more dedicated RAID 10 spindles for tempdb and the log files, then I would tell him to go for it IF it’s a decent DAS with decent cache, controllers, etc. Find out what the SAN and DAS are and how they’re configured. We can then give you a better idea if this is going to work. You can’t just make a blanket statement that "NAS is better than SAN" for a situation like this. You need to know how both are configured and what he’s really giving you. MeanOldDBA [email protected] When life gives you a lemon, fire the DBA.

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