Storage Management Strategies for the CIO
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Linear Tape File System (LTFS)
You don’t often find the words “tape” and “exciting” in the same sentence. But if there were an occasion sufficient to run those two words together, it would be the advent of LTFS. LTFS, originally
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developed by IBM and adopted by the LTO Consortium, is a self-describing file system
that makes files on tape directly host-readable. The file system metadata tracks the media element,
location of the tape and data location on tape. LTFS-enabled apps can request a tape load from a
library, provided the library supports LTFS.
LTFS is arguably the most exciting tape development since the advent of cartridges and robots. LTFS and related device drivers are available as free downloads from numerous vendors. Because it’s a file system, its directory structure is directly readable. Users are no longer dependent upon third-party software to read the tape. They can use standard file operations on the files even though they reside on tape. For example, HP offers both StoreOpen Standalone for standalone tape drives in a MAC OS X environment as well as StoreOpen Automation. StoreOpen Automation presents the tape library and cartridges as a collection of folders; media movement is handled automatically by the application.
LTFS is targeted primarily at unstructured data, especially files that are unlikely to change. Files on disk may be modified, even when a contiguous block isn’t available, simply by using pointers. The notion of pointers skipping from one tape block to another to retrieve a complete record is currently antithetical to tape. Even if one were able to span media elements with a single file (which can’t be done), loading multiple tapes to retrieve a single file might not yield acceptable performance.
Because files are host accessible, LTFS does provide nearline storage. Examples of ideal candidates for LTFS are medical images and video files. Medical images, in particular, are never modified. Storing these large files benefits from the low cost of tape, yet they can be found and accessed directly by users. The time needed to load the file from tape will be longer than with disk, but shorter than if the file were stored offline.
This was first published in February 2012
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