deb9 - strange tar behavior

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Re: deb9 - strange tar behavior

Postby llivv » 2019-01-05 02:16

ksu wrote:I still don't get this...

I need to start understanding this one way or another - "debugging a script" does not provide me with answer to the tar behavior question

Correct, debugging the script does not answer your question concerning the tar behavior.

Are you still trying to send a tarball to a remote hosts tape drive?
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Re: deb9 - strange tar behavior

Postby ksu » 2019-01-05 02:47

yes, I am still trying to send the tarball, using mbuffer... in many cases it does prevent buffer underruns, it depends on the tape drive/tape type ( LTO-3...5 ), the type of data it is dealing with ( I rather do compression on a multicore system, than let the data being dealt with on the h/w provided compression ), plus it also gives me choice of using a different compression algorithm.... on small amounts of data, the improvement is questionable and often shows disadvantage, but I confirmed the backup to be much quicker when the tape drive does not get to buffer underruns... it stops being a "streamer" and continues to re-position the tape... this is not only bad for performance, but for the hardware/media itself. Adding eg. 8GB of buffer on both ends either prevents this from happening completely, or minimizes it.

I have no issue using the old version of tar for this purpose, but then this becomes limited to availability of tar (or even gcc) on a specific system.

What bothers me, is the difference of behavior directly from shell, and script... debugging might become a nightmare when dealing with similar cases, and maybe there is a single explanation that could potentially be applied to similar cases - I just wish/want to get to the bottom of it... it always helps when you know the cause, rather than just look for a workaround...

Thanks!
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Re: deb9 - strange tar behavior

Postby llivv » 2019-01-05 19:21

sorry if not being clear enough....
My next step would be to
sending a test tarball from each tar version to the remote hosts tape
both with and without mbuffer
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