> The file system that has come closest to our design principles, other than ZFS itself,is WAFL[8],the file system used internally by Network Appliance’s NFS server appliances.
That was unnecessary, but that does not betray even the slightest risk of violating NetApp's patents. It just brings attention.
Also, it's not true! The BSD 4.4 log-structured filesystem is such a close analog to ZFS that I think it's clear that it "has come closest to our design principles". I guess Bonwick et. al. were not really aware of LFS. Sad.
LFS had:
- "write anywhere"
- "inode file"
- copy on write
LFS did not have:
- checksumming
- snapshots and cloning
- volume management
And the free space management story on LFS was incomplete.
So ZFS can be seen as adding to LFS these things:
- checksumming
- birth transaction IDs
- snapshots, cloning, and later dedup
- proper free space management
- volume management, vdevs, raidz
I'm not familiar enough with WAFL to say how much overlap there is with WAFL, but I know that LFS long predates WAFL and ZFS. LFS was prior art! Plus there was lots of literature on copy-on-write b-trees and such in the 80s, so there was lots of prior art in that space.
Even content-addressed storage (CAS) (which ZFS isn't quite) had prior art.
> I guess Bonwick et. al. were not really aware of LFS. Sad.
They were:
> [16] Mendel Rosenblum and John K. Ousterhout. The design and implementation of a log-structured file system. ACM Transactions on Computer Systems, 10(1):26–52, 1992.
> [17] Margo Seltzer, Keith Bostic, Marshall K. McKusick, and Carl Staelin. An implementation of a log-structured file system for UNIX. In Proceedings of the 1993 USENIX Winter Technical Conference, 1993.
That was unnecessary, but that does not betray even the slightest risk of violating NetApp's patents. It just brings attention.
Also, it's not true! The BSD 4.4 log-structured filesystem is such a close analog to ZFS that I think it's clear that it "has come closest to our design principles". I guess Bonwick et. al. were not really aware of LFS. Sad.
LFS had:
LFS did not have: And the free space management story on LFS was incomplete.So ZFS can be seen as adding to LFS these things:
I'm not familiar enough with WAFL to say how much overlap there is with WAFL, but I know that LFS long predates WAFL and ZFS. LFS was prior art! Plus there was lots of literature on copy-on-write b-trees and such in the 80s, so there was lots of prior art in that space.Even content-addressed storage (CAS) (which ZFS isn't quite) had prior art.