LTO capacities (planning with native TB)

Native vs “compressed” capacity

LTO marketing typically lists two capacities:

Native (uncompressed): physical capacity of the cartridge.
Compressed: assumes data compresses well (often quoted as 2.5:1). Media files and encrypted data usually do not.

Generations (common ones)

Generation	Native per cartridge	“Compressed” (typical claim)	Notes
LTO-7	6 TB	15 TB	Older but still in the wild.
LTO-8	12 TB	30 TB	Common used-market sweet spot. See: lto.org LTO-8
LTO-9	18 TB	45 TB	High value per TB in many markets.
LTO-10	30 TB	75 TB	Latest generation; 400 MB/s native. See: lto.org LTO-10
LTO-10 (newer cartridge spec)	40 TB	100 TB	Same drive generation; newer media spec.

Tape count math (rules of thumb)

Tapes needed ≈ (dataset TB / tape native TB) rounded up, plus spares.
Add overhead for verification reads, rotation, and operational convenience (keeping active sets loaded in a library).
If you need GFS retention, plan separate pools: weekly, monthly, quarterly, annual.

Example

500 TB archive set:
  LTO-8  (12 TB native): 500/12  = 41.7 -> ~42 tapes
  LTO-10 (30 TB native): 500/30  = 16.7 -> ~17 tapes
  LTO-10 (40 TB native): 500/40  = 12.5 -> ~13 tapes

20 TB frequently-changing set (weekly full-to-tape example):
  LTO-8  : 20/12 = 1.7 -> ~2 tapes per weekly full
  LTO-10 : 20/30 = 0.7 -> ~1 tape per weekly full

If you want tighter numbers, measure daily change rates and decide whether you write daily-to-tape or daily-to-disk then weekly-to-tape (often cheaper).