The original ZFS paper references WAFL wrt its similarity a number of times. It seems like the biggest distinction that the paper claimed was that ZFS had pooled storage and WAFL was network oriented.

WAFL's biggest idea of the day was "write-anywhere" (the WA in WAFL). Write-anywhere is another way of phrasing copy-on-write which is a fancy way of saying _never overwrite_.

The idea, while simple, can be built upon to yield features like cheap snapshots and reasonable data integrity.

Perhaps "clone" is a bit too much but the similarity is definitely there.

FWIW, the NetApp folks sued Oracle because they also thought it looked similar [2]

[1] http://users.soe.ucsc.edu/~scott/courses/Fall04/221/zfs_over...

[2] http://www.netapp.com/us/company/news/press-releases/news-re...