When discussing design considerations for a Cloud environment there are always a few “hot” topics. Two of these usually stand out: Network and Storage.
This is not only the case with Cloud environments but with virtualization in general. I guess where Cloud differentiates itself from a regular virtual environment is storage tiering. A simple reason to implement storage tiering is cost. Running every virtual machine on the same storage is not very cost effective and will ultimately increase the prices per unit, whether that unit is a VM or consumption model based is not even important at this point.
Many storage vendors offer an automated storage tiering concept. These typically migrate virtual disks or “blocks” based on load pattern. This might be a viable solution for your enterprise environment but is that also the case for a Cloud provider? Or better said for the customers running their workload within the Cloud?
Would you want your virtual disks, or blocks, to be migrate when the storage subsystem of your provider feels it should? Or would you prefer a predictable performance? I guess I am hoping that you, as possible customers, could answer this question. Personally I prefer to get what I paid for. If I have paid for raid-5 on 15.6K disks I want to be able to use that performance when my application requires it.
Now you might say, well with the auto migration mechanism Arrays have these days you will be on fast storage before you know it, but is this actually the case? (Think EMC’s FAST, Compellent’s Data Progression or 3Par’s Adaptive Optimization) Many of these mechanisms will move data around when a threshold has been exceeded within a specific time frame. This might be too late, your job might have already completed. Now I am not, most definitely not, an expert on automated storage tiering, but I wonder who will benefit and when in the Cloud space? Maybe even more important, what if my mechanism chooses to move me to fast storage… will my Cloud service provide bill me for this?
I know I am not answering any questions here and I guess this is one of those posts which rises more questions… I would like to open the floor to anyone who wants to share his thoughts.