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what happens if LTFS on LTO loses a bit/senses corruption?

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Rachael Busher
what happens if LTFS on LTO loses a bit/senses corruption?
on Jan 12, 2018 at 2:26:52 pm

Specific post for a specific question since this board seems a little slow moving...

I'm wanting to use LTFS for file storage on LTO Ultrium tapes because i'm sold on the 'ease of use' aspect. What i'm curious about is what happens if LTO actually does have a bit of corruption somewhere... like I assume normal tape archival software potentially accounts for this (?) and would have a way to restore the 99% not negatively affected, but I was curious how a single monolithic 2.4gig file on say a 2.5gig LTO6 tape would react if a bit were missing from the middle. I assume I lose the entire file and have to go to a mirrortape or other backup?

I am aware statistically this is less likely to occur 'randomly' than on most other media, but i'm wondering if this is a potential downside of LTFS.


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Martin Greenwood
Re: what happens if LTFS on LTO loses a bit/senses corruption?
on Jan 12, 2018 at 4:29:37 pm

The short answer is that a single unrecoverable error on tape would stop the reading of that file at that point. However other files on tape would be fine. Other methods of writing files to tape like TAR would be the same or worse from a recovery standpoint.

Here is the longer answer...

Like a hard drive, the method used to organise your files on tape does not impact the error rate or recovery, as the drive doesn't know what you are writing.

There is redundant data written to allow error recovery. Again this is handled by the drive regardless of the method used to write the tape. Also unlike hard drives it's hard to write over data on a tape, it's effectively in an amend mode.

With LTFS there is also an index of files and this is written to multiple places to prevent total loss.
If you lose power whilst writing then you can repair a tape, this rolls back to the last index written.
However this is not an issue as you still have the original material at this point.

Whilst writing the drive performs a hardware verify of the data. However it makes sense to read back all the files to check that they have all been written. Software like our YoYottaID LTFS does this automatically.

If a tape is dropped or mistreated the tape can be damaged. Whilst this can cause some files to be unrecoverable, the rest of the tape will be ok.

The main thing is to have a minimum of two copies of your data. So make two tapes before you delete the originals.
Then keep them in different locations.

Martin

CTO

YoYotta.com


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Jerzy Zbyslaw
Re: what happens if LTFS on LTO loses a bit/senses corruption?
on Feb 19, 2018 at 5:51:53 am

Your best bet would be to create Par 2.0 archives using either Multipar or Quickpar so that if any of the data is missing or unreadable then it can be reconstructed https://en.wikipedia.org/wiki/Parchive


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