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docs: faq: update sparse file support, refs #14

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borg create --sparse seeks over holes, but the archive still does not
record the hole layout, so extract --sparse can not reproduce it exactly.

Co-Authored-By: Claude Opus 5.5 <[email protected]>
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Thomas Waldmann
2026-10-06 19:06:00 +02:00
co-authored by Claude Opus 5.5
parent 05302a7995
commit 8a84a81788
1 changed files with 7 additions and 4 deletions
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docs/faq.rst
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@@ -122,10 +122,13 @@ Which file types, attributes, etc. are *not* preserved?
misses a UDS!
* The precise on-disk (or rather: not-on-disk) representation of the holes
in a sparse file.
Archive creation has no special support for sparse files, holes are
backed up as (deduplicated and compressed) runs of zero bytes.
Archive extraction has optional support to extract all-zero chunks as
holes in a sparse file.
``borg create --sparse`` detects the holes and seeks over them instead of
reading them, but the archive does not record which ranges were holes:
holes are backed up as (deduplicated and compressed) runs of zero bytes,
like zero bytes that are stored in the file.
``borg extract --sparse`` creates holes from all-zero chunks, so the
extracted file can have holes where the original had stored zero bytes
and vice versa.
* Some filesystem specific attributes, like btrfs NOCOW, see :ref:`platforms`.
Are there other known limitations?