I wrote about this in 2008 on my now defunct corporate blog at NetApp. It’s fun to be working at a company that can actually create the IOPS tier.
Flash has once again thrown into stark relief the absurd classification of storage into tiers
Talk to a storage vendor and Tier 1 is their most expensive stuff. Talk to a storage architect and Tier 1 is their most expensive stuff. If you’re lucky there is some overlap.
Then we have Flash. Is it Tier 0? Does Flash make Disk Tier 5? What is the role of Flash and Disk? Is Disk the new Tape? So do we need to have Tier -1 for storage that is faster than Flash?
Then there is the whole disk storage is secondary storage. Secondary to what?
I never really did get all of those classifications of storage into tiers. I tend to think of storage in terms of how it is used.
So instead let me propose a new model for storage tiers based on the ratio of application CPU and memory, the amount of IOPS required and the capacity needs of the application or the ratio CPU:memory:IOPS:Capacity.
Based on that ratio there are three storage tiers
- Captive IOPS, where IOPS are all dedicated to a single application. In this deployment the ratio is 1:1:1:1. Add more CPU and Memory and you add more IOPS and Capacity. Because of the nature of the application and how many IOPS it consumes, there is nothing left over for another application.
- Shared IOPS, where IOPS are shared across a collection of applications. In this deployment the ratio is M:N:1:1. As you add more CPU and memory, the number of IOPS increase but not at the same rate. So you can share the IOPS across a number of applications rather than dedicating them to a single application.
- Capacity Efficient where the number of IOPS is dwarfed by the capacity requirements. In this deployment the ration M:N:1:Q. where as M and N increase, Q increases but IOPS do not. A good example is a backup server. As more data gets backed you need more capacity, but you don’t actually need more IOPS. Another good example is a home directory where capacity needs increase, but actual IOPS do not.
Next, I’ll explore the implications of these three tiers.