LTFS: Past, Present and Future by Jay Livens

LTFS or Linear Tape File System is a powerful technology that combines the economics and reliability of physical tape with the ease of data access of disk. While many industry pundits praise the solution, many end users are unfamiliar. I recently published a podcast series featuring Michael Richmond, the lead architect for LTFS at IBM. The discussions cover a range of topics related to LTFS including, specific commentary regarding the development of LTFS, how it is in use today and how Richmond envisions the technology changing in the future.

One theme that recurs throughout the podcasts is the openness of LTFS. One of the early decisions by the development team at IBM was to open source the technology to make it available for all vendors. By open sourcing the technology, IBM enabled the technology to proliferate throughout the industry, and so it is now emerged as a standard that is supported by all of the major tape vendors including IBM, HP, Quantum and Oracle. This decision was really a visionary one since it enables the benefits of LTFS to apply to all customers.

Another key element of the LTFS design was to ensure that the tapes were self-describing. Historically, tapes have been written by backup applications which are extremely powerful and typically proprietary. Hence a tape written by Symantec NetBackup would not be readable by any other backup application. This process helped Symantec optimize how data was written to tape but made it difficult for users to migrate to other solutions since all historic tapes would still need NetBackup to access them. A key element of the LTFS specification is that it mandates data formats and structures which means that an LTFS volume created by one application can be read by any other LTFS-compliant environment. This is extremely powerful and allows truly uniform LTFS readability which is critical in today's rapidly growing and heterogeneous environments.

A final theme that emerged was reliability. Tape has always been a technology for long-term storage and retention and so it is no wonder that the medium is designed to maintain data for 20+ years. Richmond and the creators of LTFS wanted to ensure that they incorporated advanced availability designs into LTFS so that it can maintain the same longevity. One of the most critical elements of LTFS is the underlying metadata stored on the tape which indicates where data is stored. The LTFS implemented a model where the most recent metadata database is stored twice, once at the front of the tape for fast access and second at the back of the tape for redundancy. Additionally, whenever changes are made, a new metadata database is written both to the front of the tape (where the previous one is overwritten) and to the end of the tape thus so past metadata databases remain on the tape. The ability to maintain previous metadata instances gives LTFS the ability to roll-back the data on the tape to a previous state much like you can do with disk array snapshots. Cool.

In short, LTFS is a very interesting technology that can completely change how you think of and use tape. I encourage you to review our podcast series with Michael Richmond on the topic. Additionally, we also created this brief whitepaper which summarizes the conversation.

LINK:	http://blogs.ironmountain.com/2014/service-lines/data-backup-and-recov...
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