Re: Couple of questions regarding dar

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 test 1 Mio Thu Apr 27
17:47:59 2017 A.rar*
*..*
*[Saved][ ][Saved][-L-][ 100%][X]  -rwxrwxr--   test test 1 Mio Thu Apr 27
17:47:59 2017 E.rar*
*No more data available from source, please do something!*
*Press return when ready to continue or hit CTRL-C to abort*

*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 test 1 Mio Thu Apr 27
17:47:59 2017 B.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?


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?

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.*


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*

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.)

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.


Am Di., 28. Apr. 2020 um 18:17 Uhr schrieb Denis Corbin <[email protected]>:

> -----BEGIN PGP SIGNED MESSAGE-----
> Hash: SHA256
>
> Hi,
>
> in complement of Mihai's explanations:
>
> 1) yes, --fs-root /foo/bar and --fs-root /foo/bar/ are equivalent
> and defines the root of the filesystem to backup (thus saved path are
> relative to it).
>
> you can restrict the backup to /foo/bar and have the "bar" part of path
> stored in the archive by doing that way:
>         dar --fs-root /foo --go-into bar
>
> it will save the same thing as using --fs-root /foo/bar but all the
> archive/backup content will be in a "bar" directory.
>
> 2) dar use an internal cache buffer, in addition compression and
> encryption algorithm, when used, also add each an additional buffer
> layer. But in any case you should see dar writing and reading
> archives/backups slices large blocks of data after large block of data
> around 51200 bytes or twice this size (it also depends on what the OS
> supports).
>
> dar_split also uses buffering (the maximum supported by the OS when
> this one provides information about that max value, else 102400 bytes)
>
> adding mbuffer between dar and dar_split does not bring performance
> gain to my point of view. As mentioned by Mihai this however will not
> cause any trouble, right.
>
> 3) in complement again, to have dar asking a password on stdin when
> creating an archive (it will do that automatically when reading an
> archive) just use '-K :' or if you want to specify the encryption
> algorithm -K aes256:
>
> You also have the possibility to add the "-K aes256:PasswordInPlainText"
> string in a file with restricted reading rights and use "-B <filename>"
> option on dar command-line. This way your password will not show on
> command-line and you can automate a backup process without worries.
>
> 4) lz4 and zstd are on the TODO list, benchmark comparative performance
> are linked to the library libdar will rely on to provide this feature.
> So if you have some info about the performances of available lz4 and
> zstd library performances let me know.
>
> 5a) by -C.. -A ... you probably mean you create an isolated catalogue
> from an backup and use that one as reference for further differential
> backup, right?
>
> you can feed these backup of their corresponding isolated catalogues
> to dar_manager. dar_manager will help you find identifying the backup
> you need to use for a given set of files (or a single file).
>
> 5b) from the outside, differential, incremental, decremental and full
> backups do not differ. This is just a dar archive format with specific
> information inside. As soon as you can set the correct tape at offset
> of the begining of a archive and upon dar_split request use the good nex
> t
> tape of the backup is split over several tapes, there should not be
> any problem if the data has not been corrupted on tape.
>
> Regards,
> Denis
>
> On 28/04/2020 00:59, Mihai Moldovan wrote:
> > * On 4/28/20 12:31 AM, Nils Privat wrote:
> >> Can I use mbuffer for it? Is anything bad with this command?
> >>
> >> dar --create - <..other options..> --fs-root /home/user1 |
> >> mbuffer -P 80 -m 2G -R 140M | dar_split split_output /dev/nst0
> >
> > Nothing obviously wrong. One issue might be that pipes itself are
> > already buffered, but that probably won't cause trouble.
> >
> >
> >> 3) To encrypt my tape backups I currently use: --key
> >> aes256:PasswordInPainText I don't like writing the password in
> >> plain text. To automate the backup a manual input is not an
> >> option. Can 'dar' read the password from file?
> >
> > This is mostly a non-issue. Since dar will take a password via
> > stdin if not provided on the command line, automation can be
> > achieved by pairing it with expect(1).
> >
> >
> >
> > Mihai
> >
> >
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