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btrfs-progs: document snapshot unaware defrag #10

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btrfs-progs: document snapshot unaware defrag #10

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11 changes: 7 additions & 4 deletions Documentation/btrfs-filesystem.asciidoc
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Original file line number Diff line number Diff line change
Expand Up @@ -55,6 +55,13 @@ if the free space is too fragmented.
Use 0 to take the kernel default, which is 256kB but may change in the future.
You can also turn on compression in defragment operations.
+
WARNING: Defragmenting with Linux kernel versions < 3.9 or ≥ 3.14-rc2 as well as
with Linux stable kernel versions ≥ 3.10.31, ≥ 3.12.12 or ≥ 3.13.4 will break up
the ref-links of CoW data (for example files copied with `cp --reflink`,
snapshots or de-duplicated data).
This may cause considerable increase of space usage depending on the broken up
ref-links.
+
`Options`
+
-v::::
Expand All @@ -79,10 +86,6 @@ target extent size, do not touch extents bigger than <size>
For <start>, <len>, <size> it is possible to append
units designator: \'K', \'M', \'G', \'T', \'P', or \'E', which represent
KiB, MiB, GiB, TiB, PiB, or EiB, respectively. Case does not matter.
+
WARNING: defragmenting with kernels up to 2.6.37 will unlink COW-ed copies of data,
don't use it if you use snapshots, have de-duplicated your data or made
copies with `cp --reflink`.

*label* [<dev>|<mountpoint>] [<newlabel>]::
Show or update the label of a filesystem.
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7 changes: 7 additions & 0 deletions Documentation/btrfs-mount.asciidoc
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Expand Up @@ -26,6 +26,13 @@ MOUNT OPTIONS
Auto defragmentation detects small random writes into files and queue
them up for the defrag process. Works best for small files;
Not well suited for large database workloads.
+
WARNING: Defragmenting with Linux kernel versions < 3.9 or ≥ 3.14-rc2 as
well as with Linux stable kernel versions ≥ 3.10.31, ≥ 3.12.12 or
≥ 3.13.4 will break up the ref-links of CoW data (for example files
copied with `cp --reflink`, snapshots or de-duplicated data).
This may cause considerable increase of space usage depending on the
broken up ref-links.

*check_int*::
*check_int_data*::
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