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docs/technical-overview: add troubleshooting section

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Hannes Laimer 2021-09-20 11:18:39 +02:00 committed by Thomas Lamprecht
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@ -164,3 +164,61 @@ Verification of encrypted chunks
For encrypted chunks, only the checksum of the original (plaintext) data is
available, making it impossible for the server (without the encryption key), to
verify its content against it. Instead only the CRC-32 checksum gets checked.
Troubleshooting
---------------
Index files(.fidx, .didx) contain information about how to rebuild a file, more precisely, they
contain an ordered list of references to the chunks the original file was split up
in. If there is something wrong with a snapshot it might be useful to find out
which chunks are referenced in this specific snapshot, and check wheather all of
them are present and intact. The command for getting the list of referenced chunks
could look something like this:
.. code-block:: console
# proxmox-backup-debug inspect file drive-scsi0.img.fidx
The same command can be used to look at .blob file, without ``--decode`` just the size
and the encryption type, if any, is printed. If ``--decode`` is set the blob file is
decoded into the specified file('-' will decode it directly into stdout).
.. code-block:: console
# proxmox-backup-debug inspect file qemu-server.conf.blob --decode -
would print the decoded contents of `qemu-server.conf.blob`. If the file you're
trying to inspect is encrypted, a path to the keyfile has to be provided using
``--keyfile``.
Checking in which index files a specific chunk file is referenced can be done
with:
.. code-block:: console
# proxmox-backup-debug inspect chunk b531d3ffc9bd7c65748a61198c060678326a431db7eded874c327b7986e595e0 --reference-filter ../../
Here ``--reference-filter`` specifies where index files should be searched, this can be an
arbitrary path. If, for some reason, the filename of the chunk was changed you can explicitly
specify the digest using ``--digest``, by default the chunk filename is used as the digest
to look for. Specifying no ``--reference-filter`` will just print the CRC and encryption status
of the chunk. You can also decode chunks, to do so ``--decode`` has to be set. If the chunk
is encrypted a ``--keyfile`` has to be provided for decoding.
Restore without a running PBS
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
It is possible to restore snapshots even without a running PBS, assuming you have
access to the index and chunk files, if encrypted you'll also need the keyfile
it was encrypted with.
.. code-block:: console
# proxmox-backup-debug recover index drive-scsi0.img.fidx ../../../.chunks
where `../../../.chunks` is the path to the directory that contains contains the
chunks and `drive-scsi0.img.fidx` is the index-file of the file you'd lile to
restore. Both paths can be absolute or relative. With ``--skip-crc`` it is possible to
disable the crc checks of the chunks, this will speed up the process, however should
probably only be used for testing.