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I've noticed that most tape drive vendors provide two options: full-height or half-height. The half-height drives are physically smaller and less expensive, yet seem to have identical specifications compared to their full-height peers.

What is the real difference between these drives? If they were really identical in operation, I'm sure that nobody would purchase the more expensive full-height drives, and they would stop being produced.

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5 Answers

up vote 6 down vote accepted

Half height used to have limited connection options, however now support almost everything full heights do. Except maybe ESCON, but if you're using that, you have bigger problems (and budgets).

The main difference between the two now is maximum speed. The tapes are the same and interchangeable, but a half height goes maybe 70% the speed as a full height. Check the vendor's published specs to be completely sure.

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The only thing you are missing is the automation of the tape being ejected from the drive. The full-height drives I have in my organization have a motor which ejects the tape nicely. The half-height drives have a door on them, you just flip it up to open it and take the tape out. IMHO, there is no difference. Our half-height perform just as well as full-height. I'm pretty sure half height was invented to save rack space. Full-height drives are obsolete in my organization now, we only buy half-height. Less moving parts to break.

Of all the tape drive failures I have dealt with, most were a full-height and

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6  
I think you accidentally the rest of you sentance... –  tombull89 Nov 8 '11 at 19:22
    
Our Quantum LTO-3 HH drive does automatic tape ejection. –  Nic Nov 8 '11 at 19:49
    
Ditto, HP LTO-3 HH does automatic –  Mark Lawrence Nov 8 '11 at 20:01
    
I would guess difference between these drives is non-existent. Basil states below a possible performance difference, I would say this is only on the theoretical maximums. The true limiting factor on tape drive performance is size and number of files on the server. That is the only piece of information that matters when determining backup speed. Full or Half Height, my drives perform between 750 and 3000 MB/min. –  Terry Zolinski Nov 8 '11 at 22:47
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Oracle SUN tape full-height supports automation environment and 8 gb/sec FC connection while half-height doesn't support these features. I guess both these features are not so important as the tape speed max is only about 120 MB/sec there is not need of FC connection.

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Oracle Sun LTO5 Half-height drives DO support both FC and SAS connections, so that's no longer the case. –  user127276 Jul 5 '12 at 18:58
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Oracle explained this in his document:

What are the differences between full-height (FH) and halfheight
(HH) drives?
Full-height drives are twice the height (2U) of the half-height
drives (1U). In addition to the differences in the height of the
drives, half-height drives historically have had lower
specifications than full-height drives. For example, LTO 4
half-height drives have a native throughput of 80 MB/s while
the full-height drive’s native throughput is 120 MB/s. With the
LTO 5 and LTO 6 releases, this trend has changed; LTO 5
half-height and full-height drives both have a native
throughput of 140 MB/s, and LTO 6 half-height and fullheight
drives both have a native throughput of 160 MB/s.

http://www.oracle.com/us/products/servers-storage/storage/tape-storage/lto-tape-drives-overview-faq-1906830.pdf

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+1. Runs down to "Historical reasons when the electronics were bigger". –  TomTom Apr 16 '13 at 8:42
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I run a tape duping company and in my experience, the full height drives are more robust, and more likely to 'go the distance' if you're operating them all day. I haven't had a chance to compare HH and FH LTO5 and 6 drives, but certainly if you disassembled earlier generations of LTO (and before that, DLT) and compared the drive mechanisms, the FH parts were stamped from thicker metal and had been finished to a higher standard.

If you're just backing up a tape or two every day, either drive will probably be swapped out and upsized before it fails; if you're using it all day every day, go for a full height.

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In my experience on 90% of drives, the first component to fail is a tape head. I don't know if the tape heads are any different between the models. –  kasperd May 29 at 12:08
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