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Linear Tape File System

File system for magnetic tape From Wikipedia, the free encyclopedia

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The Linear Tape File System (LTFS) is a file system that allows files stored on magnetic tape to be accessed in a similar fashion to those on disk or removable flash drives. It requires both a specific format of data on the tape media and software to provide a file system interface to the data.

The technology, based around a self-describing tape format developed by IBM, was adopted by the LTO Consortium in 2010.

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History

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Magnetic tape data storage has been used for over 50 years, but typically did not hold file metadata in a form easy to access or modify independent of the file content data. Often external databases were used to maintain file metadata (file names, timestamps, directory hierarchy) to hold this data but these external databases were generally not designed for interoperability and tapes might or might not contain an index of their content. In Unix-like systems, there is the tar interoperable standard, but this is not well-suited to allow modification of file metadata independent of modifying file content data - and does not maintain a central index of files nor provide a filesystem interface or characteristics.

LTFS technology was first implemented by IBM as a prototype running on Linux and Mac OS X during 2008/2009. This prototype was demonstrated at the NAB show in 2009. Based on feedback from this initial demonstration and experience within IBM the filesystem was overhauled in preparation for release as a product. The LTFS development team worked with the vendors of LTO tape products (HP and Quantum) to build support and understanding of the LTFS format and filesystem implementation leading up to the public release.

The LTFS Format Specification and filesystem implementation were released on April 12, 2010 with the support of IBM, HP, Quantum, and the LTO Consortium.[1]

LTFS v2.0.0 was released in March 2011, improving the text to clarify and remove ambiguity. It also added support for sparse files; persistent file identifiers; virtual extended attributes for filesystem metadata and control - and defined minimum and recommended blocksize values for LTFS volumes, for compatibility across various HBA hardware implementations.

LTFS v2.2.0 was released in December 2013. It was the first version to become an ISO standard (20919:2016).

LTFS v2.5.1 was released in May 2019. It became the second version of the ISO standard (20919:2021). Version 2.5 contained fairly major updates, as it was the first version to define Incremental (sparse) Indexes.

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Format specification

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The ISO/IEC 20919:2021 standard defines the LTFS Format requirements for interchanged media that claims LTFS compliance. It defines the data format, independent of the physical storage media and the software commands format, to make data truly interchangeable. The ISO standard was prepared by SNIA. It is based on LTFS v2.5.1, and was adopted to ISO by a joint technical committee ISO/IEC JTC 1 Information Technology.

The SNIA workgroup continues to develop LTFS and release updates. Version 2.0.0 defines rules for how the version number may change in future, and how compatibility is maintained across varying implementations. All implementations must:

  • correctly read media that was compliant with any prior version
  • write media that is compliant with the version they claim compliance with
More information Version, Published ...

SNIA Technical Work Group

In August 2012, SNIA announced[9] that it was forming a TWG (Technical Work Group) to continue technical development of the specification. LTFS Format Specification v 2.1 is the baseline for the technical work and standards accreditation process; SNIA LTFS TWG members include HP, IBM, Oracle and Quantum.

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Nature

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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 only deleted and capacity recovered if the whole tape is reformatted.[citation needed]

In spite of these disadvantages, there are several uses case where LTFS formatted tape is superior to spinning disk and other data storage technology. While LTO seek times can range from 10 to 100 seconds, the streaming data transfer rate can match or exceed spinning-disk data transfer rates. For example, LTO-9 is capable of a continuous transfer speed of 400 MB/s while spinning HDDs typically max out at 200–250 MB/s for the first 30% of their capacity.

Additionally, tape cartridges are easily transportable and recent tape formats hold far more data than any other removable data storage technology. The ability to copy a large file or a large selection of files (up to 30TB for LTO-10) to an LTFS formatted tape allows for easy exchange of data with a collaborator, or for saving of an archival copy.

Since LTFS is an open standard, LTFS formatted tapes are usable by a wide variety of computing systems and operating systems, avoiding the incompatibilities experienced with proprietary tape archive formats.[10]

Implementations

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Tape drives manufacturers often offer their own versions of software conforming to the LTFS standard. There are also three different editions, one for Single Drives based on the LTFS Reference Implementation, one for Tape Libraries, and one for integration into a Enterprise storage platform.

Single Drive Edition

The base form of LTFS allows tapes to be formatted as an LTFS volume, and for these volumes to be mounted - and users and applications access files and directories stored on the tape directly, including drag-and-drop of files.

Library Edition

An extension of the base form of LTFS, LTFS-LE presents a tape library full of LTFS tapes as online directories and mounts and unmounts tapes as needed. Each LTFS-formatted tape cartridge in the library appears as a separate folder under the filesystem mount point and the user or application can navigate into each of these folders to access the files stored on each tape. The LTFS-LE software automatically controls the tape library robotics to load and unload the necessary LTFS volumes.

Enterprise Edition

The Enterprise Edition integrates a large cluster filesystem, IBM's GPFS, with LTFS Library Edition, to expand a large online file system with an automatically managed tape tier. Files may be automatically migrated from disks to tapes when certain criteria are met, such as extended periods of inactivity, and recovered back to disk automatically when a user try to access them.

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LTFS compatible products

DDS Tape Drives

Enterprise Tape Drives

  • IBM:
    • TS1140, TS1150, TS1155, TS1160, TS1170, and TS1180 [13]
  • Oracle (Sun/StorageTek):
    • T10000C and T10000D [14]

LTO Tape Drives

  • HPE, IBM, Quantum, and MagStor (Overland/Tandberg):
    • from LTO-5 to LTO-10

Appliances and ISVs (Independent Software Vendors) supporting LTFS

A full set of vendors are listed at LTO website.[15]

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LTFS projects

  • Thought Equity Motion[16] is executing a major film digitization and preservation project for the EYE Film Institute Netherlands. The project involves scanning more than 150 million discrete DPX files and storing them on LTO Gen5 using the LTFS format.[17] More than 1 petabyte of film will be[needs update] scanned and archived over two years (2010–2012).

Industry recognition

  • IBM LTFS technology received a Pick Hit Award from Broadcast Engineering at NAB 2011.[18]
  • IBM and FOX Networks received an Engineering Emmy Award in 2011 for a project that uses LTFS to store, exchange, and archive video content.[19]
  • IBM received the 2011 Hollywood Post-Alliance (HPA) Engineering Excellence Award.[20]

Limitations

As of standard version 2.5.1, LTFS does not support hard links.[8]

When files are deleted, they become invisible to the user. However, the space occupied by a file is not freed. Because of this, it is possible to "roll back" the tape to an earlier state, in order to recover erroneously deleted (or incorrectly updated) files. [8] To free up space a tape needs to be re-formatted.

References

External links

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