Some customers ask us – not surprisingly – how they can reduce their total cost of ownership in their information infrastructure even more. In response, I sometimes ask them what the utilization is of their storage systems.
Their answer: often something like 70% – you need of course some spare capacity for sudden application growth, so close to 100% is probably not a good idea.
Overallocating storage
If you really measure the utilization you often find other numbers. And I don’t mean the overhead of RAID, replication, spare drives, backup copies etc. because I consider these as required technology – invisible from the applications but needed for protection and so on. So the question is – of each net gigabyte of storage, how much is actually used by all applications?
Dirty Cache 