Backup Physical Tape Restore

LTO-5 and Disk-based Backup

HP recently announced the availability of LTO-5 and they are currently hosting industry luminaries at their HP Storage Day. I received a question on Twitter from John Obeto about LTO-5 and what it means to VTL and wanted to answer it here. Note that I previously blogged about LTO-5.

The challenge with data protection is ensuring that you meet your backup and recovery requirements, and most companies have fixed SLAs. The advent of LTO-5’s larger tape sizes is nice, but tape size is not the problem, the issue is real world performance. Quantum’s LTO-5 specification suggests maximum performance of 140 MB/sec which is an impressive statistic, but in practice few end users achieve this. The challenge is even greater when you think about minimum required transfer rates as discussed in my fallacy of faster tape post

Backup Physical Tape Restore

Tale of the Tape: Musings on IBM’s 35TB Tape Announcement

A recent tweet by Chris Mellor from The Register caught my eye. He highlighted IBM’s recent development of a 35TB tape. Here are four articles on the topic:


FUJIFILM Announcement

The Register Article

A blog post by Robin Harris at ZDnet

My thoughts

It is interesting to see IBM/Fuji driving tape development. With this announcement they have increased native tape capacity over 21x from LTO-5, the newest LTO offering. The dramatic density improvement will drive a continued decrease specification-based $/GB. However it also raises some new questions:


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Streaming LTO-5

Chris Mellor (twitter:@Chris_Mellor) recently posted an article over at The Register about LTO-5 entitled Is LTO-5 the last harrah for tape?.  He makes an interesting point about the future of LTO and whether LTO-5 will be the last generation of the technology.  Most of the comments on the article disagree with Chris’s opinion.

I believe that there is another major issue with LTO-5 that must be addressed.  The challenge with LTO (and most other tape technologies) is its limited ability to throttle performance.  Users must carefully manage their environment to ensure that they stream their drives or else backup performance will decline dramatically.  As drives become faster, the challenge of optimizing your environment for the technology becomes more difficult.  You can read more about this in my blog post entitled The Fallacy of Faster Tape.

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The Fallacy of Faster Tape

I often talk about disk-based backup and virtual tape libraries (VTL) and wanted to discuss physical tape. While VTLs are popular these days, tape is still in widespread use. LTO tape, the market share leader, continues to highlight increased density and performance. Do not be fooled with these claims. In the real world faster tape often provides little or no improvement in backup and/or restore performance. Ironically, faster tape increases (not decreases) the need for high performance disk devices like VTLs. Let me explain.

Modern tape drives use a linear technology where the tape head is stationary and the tape moves at high speed above it. Through each generation of LTO, the tape speed is largely unchanged while tape density doubles. At the same time, LTO drives have not expanded their ability to vary the speed of tape. Thus if you go from LTO-3 to LTO-4, you have doubled the density of your tape and you must double the throughput of data handled by the drive to keep tape speed unchanged. Why does tape speed matter? Because LTO tapes have a limited ability to throttle tape speeds, your performance will suffer terribly if you cannot meet the drives minimum streaming requirement.

If you are unable to stream enough data to your tape drives as mentioned above, the tape drive will go into a condition called “shoe shining” where it is constantly stopping and starting. It will try to stop when its buffer empties, but the tape is moving so fast that it will overshoot its stopping point and need to slowly stop, rewind to where it stopped writing and begin writing again. The tape moves forward and backward like shoe shine cloth. This process causes a massive reduction in performance and excessive wear on the tape drives and media. The table below comes from a Quantum whitepaper entitled “When to Choose LTO-3” and highlights the real world performance requirements of LTO-2 and LTO-3. I have estimated LTO-4 requirements for completeness.