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btrfs-progs: docs: update check modes 

Signed-off-by: David Sterba <dsterba@suse.com>
This commit is contained in:
David Sterba 2019-11-05 21:58:32 +01:00
parent a999abb7e9
commit a85c496c0d
1 changed files with 16 additions and 10 deletions
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26
Documentation/btrfs-check.asciidoc
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@ -36,7 +36,8 @@ extents, backreferences, missing extents of inodes, directory and inode
connectivity etc.
The amount of memory required can be high, depending on the size of the
filesystem, similarly the run time.
filesystem, similarly the run time. Check the modes that can also affect that.
SAFE OR ADVISORY OPTIONS
------------------------
@ -113,16 +114,20 @@ build the extent tree from scratch
+
NOTE: Do not use unless you know what you're doing.
--mode=MODE::
--mode <MODE>::
select mode of operation regarding memory and IO
+
The 'MODE' can be one of 'original' and 'lowmem'. The original mode is mostly
unoptimized regarding memory consumption and can lead to out-of-memory
conditions on large filesystems. The possible workaround is to export the block
device over network to a machine with enough memory. The low memory mode is
supposed to address the memory consumption, at the cost of increased IO when it
needs to re-read blocks when needed. This may increase run time.
The 'MODE' can be one of:
+
'original'::::
The metadata are read into memory and verified, thus the requirements are high
on large filesystems and can even lead to out-of-memory conditions. The
possible workaround is to export the block device over network to a machine
with enough memory.
'lowmem'::::
This mode is supposed to address the high memory consumption at the cost of
increased IO when it needs to re-read blocks. This may increase run time.
+
NOTE: 'lowmem' mode does not work with '--repair' yet, and is still considered
experimental.
@ -132,7 +137,8 @@ quiescent or read-only mounted filesystem but may crash if the device is
changed externally, eg. by the kernel module. Repair without mount checks is
not supported right now.
+
This option skips the delay and warning in the repair mode (see '--repair')
This option also skips the delay and warning in the repair mode (see
'--repair').
EXIT STATUS
-----------