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Right Sizing ratio Physical Memory to db size

I was wondering if someone could lead me in the right direction? I have have a SQL database roughly 15gb and I am looking to spec new hardware. I would like it to perform at its maximum effeciency. Effenciency meaning, right amount of ram, proper disk array, disk speed etc. Everyone is quick to think efficiency is fast performance, it is in some scenario I guess but I am looking for the even plane, not to hard on the disks, users don’t suffer long delays etc. The data base has an applciation attached to it, only one conncetion that handles all the calls to is. It is mainly storing constant information that gets updated when the users are not on it. So the intense processing is at night when it is updating or indexing records. With the expected growth over 5 years to be another 10gb is it safe to say load up on the RAM or better yet how do I rationalize what should be considered. Thank you for your time.

It’s really hard to make a suggestion without knowing the application and how it works. It depends on many factors. Go with a moderatly new server (Dual Core or dual processors, 2-4 GB RAM) and a good disk sub system to begin with if you have no data to go on. Any redundancy is usually a plus (power, disk, network, battery cache etc). If you have an old environment then monitor it to give you a hint in the right direction as well.
How much RAM does your current system have, what is the current buffer cache hit ratio, and how many available bytes does the system have? If this buffer hit cache ratio is over 99%, and the available bytes is over 5MB, then most likely, more RAM won’t make much difference in the current performance, although you may want to add more to deal with future needs. In regards to disk I/O, are there any current bottlenecks? If not, then the hardware you have is fine for what you are doing now. But if you want to plan an "ideal" system that will meet future needs, try to go for a RAID 10 system, and divide the data and log storage between two different arrays, and put the OS and SQL bininaries on a RAID 1 or RAID 10 array. —————————–
Brad M. McGehee, SQL Server MVP