Netapp has been on the hot seat ever since Tom Georgens, their CEO commented that tiering would soon be obsolete. Since then, a number of people have called him out on it, including yours truly (in a steering wheel cam), StorageBod, The Storage Architect, StorageZilla , a storage blogging wannabe, and last but not least, the Storage Anarchist. To be fair, Georgens DID get support from the contrarian Drunken Data.
At the end of his post, the Storage Anarchist asks:
It's tempting to suspect WAFL's snapshot mechanism is the problem, but there is nothing about file level snapshots that would preclude storage tiering. Storage tiering depends on the ability to redirect block addresses across devices classes, which can be done at an abstraction layer below the file system level. In Netapp's case, the issue appears to be an interlock between WAFL and Netapp's underlying RAID layer. So I'd say its mostly a Netapp RAID problem.
As writes come into a WAFL system, they are first staged to NVRAM in order to eliminate parity RAID write penalties and then they are written to "nearby" blocks using a tightly coupled relationship between the file system and its underlying RAID subsystem. This design has an unusual and intricate knowledge of disk drive operations and status within the RAID array. In other words, the file system in a Netapp machine is intricately coupled to the physical characteristics of the underlying storage hardware, which means creating block abstraction layers is highly improbable. The text-image below is from Netapp's Patent filing 6,138,126 dated October 24, 2000.
Now it's possible that this patent does not indicate the implementation within Filers today, but I'd say there is a good chance it explains Netapp's reluctance to embrace tiering. If this turns out to be Netapp's tiering shortcoming, Netapp would need to virtualize their RAID implementation in order to get to a point where they could start working on tiering.
Holy cow!! Is it possible that Netapp is actually THAT FAR behind in storage virtualization - not to mention the next wave of the technology - tiering?
If this analysis is correct, it may be that the only way to get tiering (not caching) with a Netapp system is to connect their V-Series filer to a third party array that offers tiering. If that's the case, will Netapp support it, seeing as how they don't have it on their home-grown Filers?
The hot seat could get a lot hotter.