Both an autoloader and a tape library save someone from changing a cartridge every evening: a robot moves tapes between storage slots and a drive. The difference is scale and flexibility. An autoloader is a small box with one drive and a magazine or two of tapes. A tape library has many slots, several drives writing in parallel, and features such as partitions and in-library vaulting. Which you need comes down to four numbers you already know.
What an autoloader is
An autoloader is the smallest form of tape automation. It holds one tape drive and a fixed number of cartridges, usually in removable magazines, with a robot that loads the next tape when the current one is full or a new job starts. Quantum’s SuperLoader 3 is a typical example: a 2U rack unit with one half-height LTO drive and one or two 8-cartridge magazines, so 8 or 16 tapes in all.
Because there is only one drive, an autoloader does one thing at a time. It can run a nightly backup unattended for a week or more, swap in a cleaning cartridge, and read barcodes so the backup software knows which tape is which. It cannot run two jobs on separate drives, so a restore has to wait for a running backup or interrupt it.
What a tape library adds
A library is the same idea with more of everything, and that changes what it can do. Quantum’s Scalar i3, the smallest of its libraries, starts at 25 slots in one 3U module and grows to 800 slots and up to 24 drives in 48U of rack. Larger libraries go further: the Scalar i6000 reaches 14,100 slots and 192 drives.
Three capabilities come with that scale. Several drives can write in parallel, which shortens the backup window. The library can be split into partitions, so different backup applications or departments share one robot without seeing each other’s tapes. And libraries offer features for keeping tapes offline inside the box, such as Quantum’s Active Vault, which moves exported tapes into a partition with no drives and no host connection. See Scalar Active Vault and Ransom Block.
The four numbers that decide it
You can settle the question with arithmetic rather than a product sheet. Work out these four figures for your own backups:
- •Cartridges you need online: the tapes in your current retention cycle that must sit in the unit, plus scratch tapes and a cleaning cartridge. More than 16 rules out a 16-slot autoloader.
- •Drive-hours per full backup: full size divided by drive speed. A half-height LTO-9 drive writes 300 MB/s native, about 1.08 TB an hour, so a 20 TB full is roughly 18.5 drive-hours.
- •Your backup window: if the drive-hours do not fit the window on one drive, you need more drives, and only a library has them.
- •How many applications share it: more than one backup application, or a separate archive workflow, points to a library with partitions.
Worked example: where the autoloader runs out
Illustrative arithmetic: take one half-height LTO-9 drive at 300 MB/s native. In an 8-hour night it can write about 8.6 TB; across a 48-hour weekend about 52 TB. Those are native figures with the backup server keeping the drive streaming, which is the best case.
So an autoloader comfortably covers a site whose weekly full is a few terabytes and whose daily incrementals are smaller still. A 16-slot autoloader with LTO-9 holds 288 TB native, which is plenty of capacity for that site. The limit you hit first is usually time, not space: once the weekly full needs more drive-hours than the weekend gives you, the only fix is a second drive, and that means a library.
The other common trigger is cartridges. Four weekly fulls of 6 TB fit on four LTO-9 cartridges. But if your backup software starts each nightly incremental on its own tape, as many media-pool settings do, six nightly incrementals a week for four weeks add another 24, and you are past 16 slots before counting scratch tapes, a cleaning cartridge or any monthly copies. Appending incrementals to shared tapes cuts the count; otherwise the choice is between rotating magazines out every week or moving to a library that holds the whole cycle.
View the data behind this chart
| Standalone drive | Autoloader | Tape library | |
|---|---|---|---|
| Drives | 1 | 1 | Several |
| Cartridges online | 1 | 8 or 16 | 25 to thousands |
| Tape changes | By hand | Robot | Robot |
| Parallel jobs | No | No | Yes |
| Partitions | No | No | Yes |
| Offline copy | Remove tape | Remove magazine | In-library vault |
When an autoloader is the right answer
Autoloaders suit small offices, branch sites and single servers with a modest dataset and one backup application. They are simple, compact and quick to install, and their removable magazines make the offline copy easy: take one magazine out each week and store it away from the network. Quantum built the SuperLoader 3 for exactly this, small and remote sites with limited IT staff.
They also make sense alongside disk. Many sites back up to a disk repository every night and copy only the weekly full to tape, which keeps the tape job inside one drive’s reach. See tape vs disk vs cloud for how the tiers fit together.
When to go straight to a library
Buy a library when any of these is true: your weekly full will not fit the window on one drive, you need more than 16 cartridges online, two or more applications must share the hardware, or you want the offline copy to stay inside the unit rather than on a shelf. A modular library such as the Scalar i3 also lets you license slots as you grow, in 25-slot steps, so buying a library early does not mean paying for capacity you will not use for years.
Plan the drive generation at the same time. LTO-9 drives read and write LTO-8 tapes as well; LTO-10 drives read and write only LTO-10 cartridges, and in Quantum’s range they are full-height drives for the larger libraries only. If you hold older tapes you still need to restore, see LTO drives and media.