Archive to Disk100TB for 0.5M$ + 1.5 “free” petabytes
If you have 100 TB active you need 10,000 mirrored disk arms (see tpcC)
So you have 1.6 PB of (mirrored) storage (160GB drives)
Use the “empty” 95% for archive storage.
No extra space or extra power cost.
Very fast access (milliseconds vs hours).
Snapshot is read-only (software enforced _)
Makes Admin easy (saves people costs)