BlockStore: File System in a File
Applications often have to satisfy two conflicting requirements. On the one hand the data created by a user has a structure whose parts should be managed independently of one another, ideally with each piece placed in its own file. On the other hand users like to think of their data as a single entity which can be copied, emailed and backed up in its entirety. Although Mac OS X has the notion of a bundle, a specially marked directory which behaves like a single file when manipulated by the Finder, other operating systems do not.
So, a ZBlockStore takes a single file (or file-like entity) and allows an application to work with resizable blocks allocated within it, easily, efficiently and (with ZBlockStore_PhaseTree) safely.
- Easy to use — blocks are managed with the same API as real files.
- Efficient — all the data lives in a wide fan-out B+ Tree.
- Safe — modifications to nodes in the tree cause the entire ancestor branch to be replicated into existing free space, and the new root is atomically updated only when descendant nodes are known to be in stable storage.
