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Copy-on-write snapshots consume space in proportion to changed blocks, not volume size, so a 500 GB volume changing 4 percent daily accumulates about 20 GB per daily snapshot. Retaining fourteen of them costs 280 GB — over half the volume — which is why snapshot retention on a write-heavy volume needs explicit capacity planning.
Snapshot space
space per snapshot = volume x daily change rate x (interval / 24); total = space per snapshot x snapshots retained
Because overwriting the same block repeatedly creates a new copy each snapshot period, and because copy-on-write granularity means a small change can copy a whole block.
No. They usually live on the same storage, so a device failure or a full-volume corruption takes them with it. They are for fast rollback, not disaster recovery.