Editing Linear Tape-Open (section)

== Optional technology ==

The original release of LTO technology defined an optional data compression feature. Subsequent generations of LTO have introduced new technologies, including WORM, encryption, and partitioning features. These features are built into the drives and/or tapes and can be ignored or enabled. Compression and encryption can also be performed in software prior to the data being sent to the tape drive. However, the partitioning function can only be done in hardware, and the WORM feature requires special WORM tapes.

=== Compression ===
The original LTO specification describes a [[Lossless compression|data compression method]] '''LTO-DC''', also called Streaming Lossless Data Compression (SLDC).<ref name="SLDC"/><ref name="ECMA-321"/> It is very similar to the algorithm ALDC<ref name="ALDC"/> which is a variation of [[Lempel–Ziv–Stac|LZS]]. LTO-1 through LTO-5 are advertised as achieving a "2:1" compression ratio, while LTO-6 and LTO-7,<ref name="lto7lic"/> which apply a modified SLDC algorithm using a larger history buffer, are advertised as having a "2.5:1" ratio. This is inferior to slower algorithms such as [[gzip]], but similar to [[lzop]] and the high speed algorithms built into other tape drives. The actually achievable ratio generally depends on the compressibility of the data, e.g. for precompressed data such as ZIP files, [[JPEG]] images, and [[MPEG]] video or audio the ratio will be close to or equal to 1:1.

=== WORM ===
New for LTO-3 was [[write once read many]] (WORM) capability. This is useful for legal record keeping, and for protection from accidental or intentional erasure, for example from [[ransomware]], or simply human error. Standard LTO cartridges do include a write-protect switch in the bottom-left corner, although it is easily overridden by the user and doesn't provide any protection from accidental deletion by, for example, misidentification of a cartridge. An LTO-3 or later drive will not erase or overwrite data on a WORM cartridge, but will read it. A WORM cartridge is identical to a normal tape cartridge of the same generation with the following exceptions: the cartridge memory identifies it to the drive as WORM, the servo tracks are slightly different to allow verification that data has not been modified, the bottom half of the cartridge shell is gray,<ref name="PVMatrix"/> and it may come with tamper-proof screws.<ref name="LTO 3 WORM"/> WORM-capable drives immediately recognize WORM cartridges and include a unique WORM ID with every dataset written to the tape. There is nothing different about the tape medium in a WORM cartridge.

=== Encryption ===
The LTO-4 specification added a feature to allow LTO-4 drives to encrypt data before it is written to tape.<ref name="LTO-4 encryption"/> All LTO-4 drives must be aware of encrypted tapes, but are not required to support the encryption process. All current LTO manufacturers support encryption natively enabled in the tape drives using Application Managed Encryption (AME). The algorithm used by LTO-4 is [[Advanced Encryption Standard|AES]]-[[Galois/Counter Mode|GCM]], which is an authenticated, symmetric block cipher. The same key is used to encrypt and decrypt data, and the algorithm can detect tampering with the data. Tape drives, tape libraries, and backup software can request and exchange encryption keys using either proprietary protocols, or an open standard like [[OASIS (organization)|OASIS]]'s [[Key Management Interoperability Protocol]].

=== Partitioning ===
The LTO-5 specification introduced the partitioning feature that allows a tape to be divided into two separately writable areas, known as partitions. LTO-6 extends the specification to allow 4 separate partitions. The [[Linear Tape File System]] (LTFS) is a self-describing tape format and file system made possible by the partition feature. File data and filesystem [[metadata]] are stored in separate partitions on the tape. The metadata, which uses a standard [[XML Schema (W3C)|XML schema]], is readable by any LTFS-aware system and can be modified separately from the data it describes. The Linear Tape File System Technical Work Group of the [[Storage Networking Industry Association]] (SNIA) works on the development of the format for LTFS.<ref name="LTFS"/> Without LTFS, data is generally written to tape as a sequence of nameless "files", or data blocks, separated by "filemarks". Each file is typically an archive of data organized using some variation of [[tar (computing)|tar]] format or proprietary container formats developed for and used by backup programs. In contrast, LTFS utilizes an XML-based index file to present the copied files as if organized into directories. This means LTFS-formatted tape media can be used similarly to other removable media ([[USB flash drive]], [[external hard disk drive]], and so on). While LTFS can make a tape appear to behave like a disk, it does not change the fundamentally sequential nature of tape. Files are always appended to the end of the tape. If a file is modified and overwritten or removed from the volume, the associated tape blocks used are not freed up: they are simply marked as unavailable, and the used volume capacity is not recovered. Data is deleted and capacity recovered only if the whole tape is reformatted.{{citation needed|date=October 2015}} In spite of these disadvantages, there are several use cases where LTFS-formatted tape is superior to disk and other data storage technologies. While LTO seek times can range from 10 to 100 seconds, the streaming data transfer rate can match or exceed disk data transfer rates. Additionally, LTO cartridges are easily transportable and the latest generation can hold more data than other removable data storage formats. The ability to copy a large file or a large selection of files (up to 1.5&nbsp;TB for LTO-5 or 2.5&nbsp;TB for LTO-6) to an LTFS-formatted tape, allows easy exchange of data to a collaborator or saving of an archival copy.