Re: Couple of questions regarding dar

In Addition my testing with dar --test with tape:
https://pastebin.com/LTBkPX6G

Am Sa., 9. Mai 2020 um 23:53 Uhr schrieb Nils Privat <[email protected]>:

> Hello,
> thanks for your answer.
> I am using dar v2.6.2 (from debian repo).
>
> Maybe it helps when i am explain my testing in more detail:
>
> A) First i test dar without tape, just with regular archive files.
> From my testing everything seems to work fine, see my script / log:
> https://pastebin.com/bS02nTZz
> As you can see i created a full backup, then i renamed a folder and
> removed a file.
> After that i created a differential backup and 'dar --list' is correctly
> showing the
> renamed folder as new files and the "REMOVED ENTIES".
> Lastly i restored the full backup and it correctly restored all
> full-backup files.
> Then, after restoring the differential backup, the file '1.rar' and dir
> 'A' are deleted
> and the new dir 'Z' is restored. Everything like expected - works!
>
>
> B) Now, I used the same files and mainly the same script, but the target
> was a tape.
> See script with tape: https://pastebin.com/KiK5YnSn
> (Of course I have adjusted the commands for the use of tape accordingly).
>
> Some of my questions regarding the script and command outputs:
> 1) The listing from catalogue is like expected (see lines 274-301). Why
> the listing from tape is so different (see lines 315-418)?
> 1a) Why i got "Error while listing archive contents: elastic buffer
> incoherent structure" (line 336)?
> (My guess is the following: dar_split successfully read the content from
> the tape and after reaching EOF on tape, dar_split stops and prints "no
> more data available".
> If i am not changing the tape and just pressing ENTER, dar_split tries to
> read further and prints the mentioned error. (FYI: this error message
> doesnt occur without using encryption after pressing ENTER).
> If my assumption is correct, that dar_split tries to read further, why it
> does not just print the content of the next file (in my case the
> differential backup, which is the next file after the full backup).
> 1b) Why i do not see the "REMOVED ENTIES" when i am listing from tape but
> from catalogue/regular archive files (see line 395)?
> 2) Why restoring the differential backup from tape does not deleted files
> (see line 457-482)? I my first example A), they were deleted.
> 3) How do i interpret the testing in line 484-522 ?
> 4) More like a general question: No matter if i read, test or restore a
> backup from tape, if dar_split reaches and EOF or the end of the tape, it
> prints "No more data available from source, please do something!" and
> the user must interact. If we to not want to change or reposition the tape
> because all data is read, that is the right way to exit the commands?
> "CTRL-C" print messages like "Archive delayed termination engaged.
> Disabling signal handler, the next time this signal is received the program
> will abort immediately."
> which does not seem the right way and pressing ENTER results in other
> messages like "elastic buffer incoherent structure" because dar_split seems
> to read further.
>
> Thank you for your help in advance.
> Still hoping to use dar as my primary tape backup tool :)
>
> Am Di., 5. Mai 2020 um 21:49 Uhr schrieb Denis Corbin <[email protected]>:
>
>> -----BEGIN PGP SIGNED MESSAGE-----
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>> On 03/05/2020 11:45, Nils Privat wrote:
>> > Hello,
>>
>> Hello,
>>
>> >
>> > much thanks for your answer.
>> >
>> > During testing a few new questions have arised.
>> >
>> > 1) To list archives i run:
>> >
>> > *dar_split split_input $TAPE | dar --list - --sequential-read*
>> >
>> > *Output:* * * *[Data ][D][ EA  ][FSA][Compr][S]| Permission | User
>> > | Group | Size |          Date                 |    filename*
>> > *--------------------------------+------------+-------+-------+-------
>> - --+-------------------------------+------------*
>> >
>> >
>> *[Saved][ ][Saved][-L-][ 100%][X]  -rwxrwxr--   test test1 MioThu Apr 27
>> > 17:47:59 2017A.rar* *..* *[Saved][ ][Saved][-L-][ 100%][X]
>> > -rwxrwxr--   test test1 MioThu Apr 27 17:47:59 2017E.rar* *No more
>> > data available from source, please do something!* *Press return
>> > when ready to continue or hit CTRL-C to abort* *
>>
>> I guess you have to change of tape, then hit return for dar_split read
>> the next part of the archive
>>
>> > * *No more data available from source, please do something!* *Press
>> > return when ready to continue or hit CTRL-C to abort* *^CReceived
>> > signal: Interrupt* *Archive delayed termination engaged* *Disabling
>> > signal handler, the next time this signal is received the program
>> > will abort immediately* *[Saved][ ][Saved][-L-][ 100%][X]
>> > -rwxrwxr--   test test1 MioThu Apr 27 17:47:59 2017B.rar*
>> >
>> >
>> > As you can see listing is working but i worry about that first it
>> > says "No more data available from source, please do something",
>> > then after pressing CTRL-C or enter one last entry of the listing
>> > is still printing "B.rar". Is that normal? Why not all items are
>> > listed together?
>>
>> this is the drawback of using tapes, as tape per nature provide
>> sequential read/write operations (OK you can rewind and fast forward a
>> tape, but as you have no offset information, this is not efficient to
>> randomly read or write data whenever possible).
>> So you have to provide the whole archive for dar to read its whole
>> content. If the archive has been split over several tapes you will
>> have to provide all tapes in the same order (and assume the are
>> rewinded at
>> the position where you have started writing the achive).
>>
>> You still have the possibility to isolate a archive (on fly or
>> afterward) to ease the listing as well as differential/incremental backu
>> ps
>>
>> >
>> >
>> > 2) Question regarding differential archives on tapes:
>> >
>> > I am using this command to create a full backup to tape:
>> >
>> > *dar --create - \* *--verbose=all \* *--compression gzip:3 \*
>> > *--alter=no-case \* *-Z "*.zip" -Z "*.rar" -Z "*.gz" -Z "*.7z" -Z
>> > "*.iso" \* *-X ".DS_Store" \* *--key aes256:MyKey \*
>> > *--on-fly-isolate /root/dar_catalog_full \* *--fs-root ${MY_PATH} |
>> > mbuffer -P 80 -m 4G -R 140M | dar_split split_output ${TAPE}*
>> >
>> > For differential backup i use the same command but with:
>> >
>> > *-A /root/dar_catalog_full \* *--on-fly-isolate
>> > /root/dar_catalog_d1 \*
>> >
>> > Do i have to run *'mt -f $TAPE eod'* or 'eof' between each new
>> > backup? Or is dar positioning the tape after a backup already to
>> > the end and is writing an EOF mark so i just can append a new
>> > backup?
>>
>> dar and dar_split does not know about magnetic tape (mt) specific EOF
>> marks (this is media specific). So yes, you should add after one using
>> 'mt' after the end of an archive, espetially if you plan to add
>> another backup or file after this one on the same tape.
>>
>> >
>> > INFO: After creating the first backup i checked the position: *mt
>> > -f $TAPE status* *File number=1, block number=0, partition=0.* So
>> > it seems like dar has written and EOF to file 0 and now i am on
>> > position/file=1, but executing *'mt -f $TAPE eod' *then shows:
>> > *File number=1, block number=-1, partition=0.*
>>
>> first this is dar_split that writes to the tape special device. And
>> double checking dar_split code, once all bytes are written, dar syncs
>> (should be useless for tape but it does not hurt) then just closes the
>> file it was writing to. This should not set a mt EOF mark AFAIK.
>>
>> >
>> >
>> > 3) Question regarding encryption:
>> >
>> > I create encrypted archives with the command above, rewind the
>> > tape, and list via:
>> >
>> > *dar_split split_input $TAPE | dar --list - --sequential-read
>> > --key aes256:MyKey*
>>
>> for reading you don't need to use --key option (but you can) if you
>> prefer to have your password visibile to all on process command line ;)
>>
>> >
>> > After pressing ENTER I got: *_Error while listing archive contents:
>> > too large elastic buffer or elastic buffer incoherent structure_*
>> > (I am not getting this message when i am pressing CTRL-C after
>> > listing.)
>>
>> this is either a wrong password, a wrong offset of the tape, or some
>> other incoherence between the creation time and reading time.
>>
>> I've just tested this using a named pipe (mkfifo) to emulate a tape
>> and could create and read an ecrypted archive without problem. This is
>> not likely to be a bug, which version are you using by the way?
>>
>> >
>> > If I am not using encryption/compression at all and do the same
>> > thing, i dont get the Error either by pressing ENTER or CTRL-C. It
>> > just exists the listing normally back up shell. Why am i getting
>> > the error?
>> >
>> > Much thanks for your help.
>> >
>> >
>> [...]
>>
>> Cheers,
>> Denis
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>>
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