Multilayer storage
Virtualization increases the complexity of monitoring storage performance. Just like memory, where we have more than one level, we have three levels for storage. At the highest level, we have VMs. A VM typically has two to three virtual disks (or RDMs), such as an OS drive, paging file drive, and data drive. A large database VM will have even more.
We are interested in data both at the VM level and at the individual virtual disk level. If you are running a VM with a large data drive (for example, an Oracle database), the performance of the data drive is what the VM owner cares about the most. At the VM level, you get the average of all drives; hence, the performance issue could be masked out.
Below the VM level, we have the datastore level. What you can see at this level and, hence, how you monitor, depends on the storage architecture. We will cover the centralized storage architecture first as it is a more deployment. We will cover the distributed architecture separately...
