The solution
In 1992 Dave Hitz, James Lau and Michael Malcolm founded Network Appliance to build a dedicated NFS file server. Nightly backups of Unix file systems meant hours of copying or tape, and after a crash, consistency checks could take as long as the downtime itself.
Their 1994 USENIX paper introduced WAFL: the file system writes anywhere and keeps the old root in place, so a Snapshot is a read-only clone created in an instant by copying a pointer. Copy-on-write means snapshots consume space only as blocks diverge; WAFL keeps up to 20 scheduled snapshots online and exposes them through a .snapshot directory so users can recover deleted files themselves.
The same mechanism eliminated long consistency checks after unclean shutdowns, a key selling point for the appliance. NetApp's Snapshot feature became an industry standard; the company IPO'd in 1995, grew past $1 billion in revenue and became the leading NAS supplier.
What it achieved
Never overwrite; snapshot is a pointer
Why it worked
A snapshot is a pointer copy, so creating it takes milliseconds, not hours.
Copy-on-write means old versions cost almost no disk until data changes.
Users recover their own deleted files via the .snapshot directory.
Fast restart after crashes removed the worst pain of file servers.
What can be applied
If the thing you dread (backup, undo, restart) is expensive, change the write path: when every change is versioned by construction, the recovery artifact is a pointer you already have.
Aftermath
Snapshots and their descendants (SnapMirror, FlexClone, deduplication) remained NetApp's product core for three decades. The 1994 paper is a classic of storage systems, and every major file system since — including ZFS and Btrfs — borrows its copy-on-write snapshot idea.
FOLLOW THE EVIDENCE