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What is best practice to maximize tape lifespan:
Append backups to the tape until it becomes full, then overwrite it before the next usage.
or
Overwrite the tape before it becomes full (for example: when used space is 70% or every month even it's not full)?
geek
Posted 2015-08-10T13:37:44.137
Reputation: 63
2
If you use only 70% of the tape, than the lifespan will be proportionally longer. However, then you have to use more tapes.
Lifespan depends on the number of end-to-end passes, that is how many times the tape was completely moved from one reel to the other.
Writing the tape to full capacity means several end-to-end passes, because only a limited number of tracks are written in a single pass. For example writing a 400GB raw capacity LTO-3 tape requires 44 passes. If you only use 70% of the tape then those data is written in 44*70%, that is about 31 passes.
You can overwrite the same place on the tape as many times as you wish, that does not seriously limit the lifespan. But moving the tape from one reel to the another does.
The Wikipedia article on LTO tapes describes this technology quite well: Linear Tape-Open
Hontvári Levente
Posted 2015-08-10T13:37:44.137
Reputation: 186
2I don't see how "if you use only 70% of the tape, the lifespan will be proportionally longer" follows from "lifespan depends on the number of passes". If anything, it would seem to me to be the opposite: using a smaller portion of the tape means you will be using that portion of the tape at least equally much, and possibly more, which by your argument would decrease the lifetime of the full tape. Can you [edit] your answer to clarify? – a CVn – 2015-08-10T20:00:22.240
I have edited the reply to clarify that a pass means completely moving the tape from one reel to another, and not the number of writes on a single point of the tape. – Hontvári Levente – 2015-08-11T04:12:42.793
Thank you guys. If I understand correctly: 400 GB / 44 passes (9 GB/Pass), so for example: First write 18 GB : +2 passes. Append 4.5 GB : +1/2 pass. Append 1 GB : +1/9 pass. Total: 2.61 passes. Write operation doesn't matter. The mechanical rewinding matters. So what is exactly a pass or even more: how do tapes work? – geek – 2015-08-11T08:58:19.483
1Jalil: that is correct. Basically the tape is divided into several tracks (704 in case of LTOL3). You put the tape cartridge into the drive and it starts to write the first set of tracks (an LTO-3 drive has 16 write heads, therefore it writes to 16 tracks at the same time). When the tape ends, that is the tape is completely winded on the internal reel, the tape switches direction. Now it writes another set of tracks while it rewinds the tape onto the reel within the cartridge. When the tape ends, the drive switches direction again and so on. – Hontvári Levente – 2015-08-11T16:25:30.880