One of the sticky wickets that holds back thin provisioning is the need to communicate when capacity is no longer needed. Enterprise storage arrays can reclaim zeroed pages, but writing all those zeros can really fill up an I/O queue. This is where WRITE_SAME comes into the picture.
Computer History
Considering the history of computing, from the enterprise to the home.
Zero Page Reclaim: Savior of Thin Provisioning?
On the storage side, arrays can only use the information they have to deallocate: The data that’s stored on them. They don’t know what application is using it, what file system it is. But, somewhere along the line, someone had a big idea and said, “wait a second, what if we look for pages that are all zeros?” We’ll talk about pages a bit later, but for now, let’s talk about zeros. A zero is kind of a smoke signal coming up from over the hills that says, “there’s nothing valuable here.”
Monitoring Filesystem Metadata For Thin Provisioning
I began by introducing the core problem: Storage isn’t getting any cheaper due to storage utilization and provisioning problems. Thin provisioning isn’t all it’s cracked up to be, since the telephone game makes de-allocation a challenge. So now let’s talk about how to make thin provisioning actually work.
Thin Provisioning: Attacking Storage Utilization
Thin provisioning doesn’t take on the cost of capacity, it actually attacks the overhead of inefficient provisioning. Not all of that overhead is inefficiency, and not all of that can be tackled with thin provisioning. But some of it can. It’s a lot more of the cost than can be tackled by moving to SATA, for example. That I really like.
Storage is Not Getting Cheaper
Why do we care about thin provisioning? Because storage is not getting cheaper. If you went to buy a disk ten years ago, you’re going to spend about the same as would today, but you’re going to get a lot more capacity – a lot more capacity! The fact that we have terrible utilization of enterprise resources is really not helping us, and it’s not getting any better. It hasn’t improved because they are “doing storage” the same way.
