I have read about it in many places and my friend Rob actually posted once here about it. Should I use SAN for my Exchange 2007? Will DAS save me money? What about performance? How do I manage storage silos? Troubleshooting complexities in SAN deployments… many questions and many views, but rarely an answer.
There is a reason for it. One cannot definitively answer this question. There are collaterals published by both Microsoft and Storage vendors. Each for obvious reasons promoting different solution.
Microsoft IT published a whitepaper that discussed how Exchange 2007 storage solution was designed and what went into the decision process. Everyone has been reading into the cost savings not realizing that’s not the only takeaway from that whitepaper. To summarize, the following factors played key role:
- Previous SAN failure and it’s impact on availability
- Dependency on another group for managing and troubleshooting storage related issues
- Scaling to higher capacity for each mailbox while controlling costs associated with storage
And these were not the only factors so don’t respond to me with list of other factors that I did not list here.
Microsoft IT deployed DAS based solution and shared their challenges, decision process and outcome along with benefits they reap from the solution implemented.
At the end of the day, the decision is going to be made based on lot of factors including business reasons. Business reasons playing a key role in decisions that will decide if you will implement SAN or DAS. Few I will list here:
- Existing investment in SAN solutions
- Existing knowledge and expertise in SAN solutions
- Management of storage (who is responsible? Application group or Storage group)
- Cost to implement DAS solution (learning curve, procedures, staff training, support)
- Operational framework and responsibilities (who should manage storage)
- Willingness of Storage group to dedicate storage and guarantee performance (dedicated disks on shared array vs. shared disks on shared array)
- SLAs, Tolerances, Dependencies, Time to recover… the list goes on
As you can see, the factors I listed above are not all technical. Business decisions are made by asking these questions along with facts that answer technical questions related to performance, MTBF, complexity to implement and manage/troubleshoot and so on.
In the end, I am not writing this post to tell you what is the best answer to DAS vs SAN debate. I am writing this to give you some questions that can help you decide for yourself what is best for your environment.
“We are our best friend or worst enemies.”
Some references to aggregate:
Some more thoughts on SAN v DAS. Is it actually time to consider DAS? – Doug Owans
Brian Henderson – Microsoft Exchange Server 2007 Storage Considerations: DAS or SAN
