Re: [Dar-support] Multiple slices on LTO6 tape
For full, incremental, compressed and encrypted backups or archives
Brought to you by:
edrusb
Menu
▾
▴
Re: [Dar-support] Multiple slices on LTO6 tape
|
From: Petr S. <sez...@se...> - 2022-06-08 19:11:32
|
Dear Denis,
I have read all the threads you mention below as well as I was searching in
dar support archive using keywords as tape LTO etc ...
I have also read a LOT of stuff about tape, mt, tar ... in general and also
on LTFS.
My conclusion is :
Your solution with symlink is NOT mentioned anywhere
I am afraid that your ide to make a symlink to block device as the tape is
wrong.
IMHO you can not use the same open file call as you do with ordinary file
backup.1.dar
So the idea (as I understand you correctly , you suggest to make a symlink
from the dumy file name - e.g. mybackup.1.dar to a tape device /dev/nst0
in order to cicumvent the problem of the filename argument - as the dar
expects the generic name mybackup as an argument .
I think this could be done by allowing the full filename as an argument
(instead of the automatic adding of .n.dar)
But anyway I am afraid the opening of the file in such way does not work
I have made an experiment
dar -c myback -R /home/skoda
dd if=myback.1.dar of=/dev/nst0
Now I make a symlink from /dev/nst0 to dummy file bigbackup.1.dar
sudo ln -s /dev/nst0 bigbackup.1.dar
Now the bigbackup.1.dar can be used instead of /dev/nst0 in command e.g.
mt -f bigbackup.1.dar status
SCSI 2 tape drive:
File number=1, block number=0, partition=0.
Tape block size 0 bytes. Density code 0x5a (LTO-6).
Soft error count since last status=0
General status bits on (81010000):
EOF ONLINE IM_REP_EN
So the link really works.
BUT not as dar argument
When I use the command you suggest
dar -C backup_isolated_cat -A bigbackup --sequential-read
or simply
dar -l bigbackup --sequential-read
the result is the same:
bigbackup.1.dar has a bad or corrupted header, please provide the correct
file. [return = YES | Esc = NO]
The reason why the header is corrupted is seen by strace
openat(AT_FDCWD, "/home/skoda/bigbackup.1.dar", O_RDONLY) = 4
fadvise64(4, 0, 0, POSIX_FADV_NORMAL) = 0
fstat(4, {st_mode=S_IFCHR|0660, st_rdev=makedev(9, 128), ...}) = 0
read(4, 0x7ffebbd5d0ac, 4) = -1 ENOMEM (Cannot allocate memory)
It is result of a call
strace dar -l bigbackup --sequential-read
As it is seen, the opening of the file causes the memory allocation problem.
So to conclude - the symlink may not be used for opening the block device in
dar.
Anyway I think the dar seems to be the best utility I have found so far -
having lot of features including the catalogue capabilities , but still very
simple for calling from command line (in comparison to complex systems as
bacula etc...)
If I can ask you for future improvement, I would suggest to modify the code
to allow reading of individual slices (i.e. tapes ) even if the content is
not consistent (i..e the slices 2 and more will have some file on the
boundary but the listing still can be done after ignoring this - when
finding next escape sequences. So each slice could be read partly to
identify what is there. It is important if you want to read a tape without
knowing what is there.
But of course it would be perfect to write a small header in each slice - so
the individual tapes could be read easily.
But I understand it is a lot of work and needs to change the dar format.
Anyway it would help a lot.
BTW - LTFS has a lot of problems - so it is not good replacement for dar on
tapes (it seems not to support multiple tapes either, moreover the symlink
and special files cannot be written - so you cannot backup the system
partition with it ...
Best regards,
Petr
---------- Původní e-mail ----------
Od: Denis Corbin <dar...@fr...>
Komu: dar...@li...
Datum: 31. 5. 2022 19:42:18
Předmět: Re: [Dar-support] Multiple slices on LTO6 tape
"Le 31/05/2022 à 02:08, Petr Skoda a écrit :
> Dear Denis,
Hi Petr,
>
> after many experiments with different block sizes and writting the
> slices either with dar_split or dd
> using your link idea below, I came to the conclusion that the things DO
> NOT WORK as you suppose (you admitted you did not have tape unit to test
> it).
Sorry to read you could not have it working. That's correct I do not
have any tape device, the information I provided was just from former
discussion with other users that had the same and approaching concern
and which gave their feedback in this mailing-list, which archive is
open and available:
https://sourceforge.net/p/dar/mailman/message/36155625/
https://sourceforge.net/p/dar/mailman/message/35548551/
https://sourceforge.net/p/dar/mailman/message/36186874/
https://sourceforge.net/p/dar/mailman/message/35030573/
https://sourceforge.net/p/dar/mailman/message/35776798/
and so on...
Maybe you can leverage the experience of others by searching the archive:
https://sourceforge.net/p/dar/mailman/dar-support/
But maybe dar/dar_split is not adapted to your need, then you will have
to find another solution.
[...]
>
> best regards,
>
> Petr Skoda
>
Cheers,
Denis
" |
