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btrfs-progs: doc: add description of missing and example, of device remove 

This patch updates help/document of "btrfs device remove" in two points:

1. Add explanation of 'missing' for 'device remove'. This is only
written in wikipage currently.
(https://btrfs.wiki.kernel.org/index.php/Using_Btrfs_with_Multiple_Devices)

2. Add example of device removal in the man document. This is because
that explanation of "remove" says "See the example section below", but
there is no example of removal currently.

Signed-off-by: Tomohiro Misono <misono.tomohiro@jp.fujitsu.com>
Reviewed-by: Satoru Takeuchi <satoru.takeuchi@gmail.com>
[ move "" from the macro to help strings ]
Signed-off-by: David Sterba <dsterba@suse.com>
master
Misono, Tomohiro 2017-10-20 10:43:05 +09:00 committed by David Sterba
parent 435145613e
commit 2192bd5cfc
2 changed files with 35 additions and 3 deletions
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29
Documentation/btrfs-device.asciidoc
View File

@ -68,13 +68,23 @@ Remove device(s) from a filesystem identified by <path>
Device removal must satisfy the profile constraints, otherwise the command
fails. The filesystem must be converted to profile(s) that would allow the
removal. This can typically happen when going down from 2 devices to 1 and
using the RAID1 profile. See the example section below.
using the RAID1 profile. See the *TYPICAL USECASES* section below.
+
The operation can take long as it needs to move all data from the device.
+
It is possible to delete the device that was used to mount the filesystem. The
device entry in mount table will be replaced by another device name with the
lowest device id.
device entry in the mount table will be replaced by another device name with
the lowest device id.
+
If the filesystem is mounted in degraded mode (-o degraded), special term
'missing' can be used for 'device'. In that case, the first device that is
described by the filesystem metadata, but not present at the mount time will be
removed.
+
NOTE: In most cases, there is only one missing device in degraded mode,
otherwise mount fails. If there are two or more devices missing (e.g. possible
in RAID6), you need specify 'missing' as many times as the number of missing
devices to remove all of them.
*delete* <device>|<devid> [<device>|<devid>...] <path>::
Alias of remove kept for backward compatibility
@ -206,6 +216,19 @@ data or the block groups occupy the whole first device.
The device size of '/dev/sdb' as seen by the filesystem remains unchanged, but
the logical space from 50-100GiB will be unused.
==== REMOVE DEVICE ====
Device removal must satisfy the profile constraints, otherwise the command
fails. For example:
$ btrfs device remove /dev/sda /mnt
ERROR: error removing device '/dev/sda': unable to go below two devices on raid1
In order to remove a device, you need to convert the profile in this case:
$ btrfs balance start -mconvert=dup -dconvert=single /mnt
$ btrfs device remove /dev/sda /mnt
DEVICE STATS
------------

9
cmds-device.c
View File

@ -224,9 +224,16 @@ static int _cmd_device_remove(int argc, char **argv,
return !!ret;
}
#define COMMON_USAGE_REMOVE_DELETE \
"If 'missing' is specified for <device>, the first device that is", \
"described by the filesystem metadata, but not present at the mount", \
"time will be removed. (only in degraded mode)"
static const char * const cmd_device_remove_usage[] = {
"btrfs device remove <device>|<devid> [<device>|<devid>...] <path>",
"Remove a device from a filesystem",
"",
COMMON_USAGE_REMOVE_DELETE,
NULL
};
@ -238,6 +245,8 @@ static int cmd_device_remove(int argc, char **argv)
static const char * const cmd_device_delete_usage[] = {
"btrfs device delete <device>|<devid> [<device>|<devid>...] <path>",
"Remove a device from a filesystem (alias of \"btrfs device remove\")",
"",
COMMON_USAGE_REMOVE_DELETE,
NULL
};