Lines Matching +full:back +full:- +full:to +full:- +full:back

4 dm_bow is a device mapper driver that uses the free space on a device to back up
6 change, or rolled back by removing the dm_bow device and running a command line
9 dm_bow has three states, set by writing ‘1’ or ‘2’ to /sys/block/dm-?/bow/state.
10 It is only possible to go from state 0 (initial state) to state 1, and then from
11 state 1 to state 2.
13 State 0: dm_bow collects all trims to the device and assumes that these mark
16 FITRIM ioctl on the file system then switch to state 1. These trims are not
17 propagated to the underlying device.
19 State 1: All writes to the device cause the underlying data to be backed up to
23 that sector 0 is used to keep a log of the latest changes, both to indicate that
24 we are in this state and to allow rollback. See below for all details. If there
25 isn't enough free space, writes are failed with -ENOSPC.
27 State 2: The transition to state 2 triggers replacing the special sector 0 with
29 becomes a pass-through driver, allowing the device to continue to be used with
34 dm-bow takes one command line parameter, the name of the underlying device.
36 dm-bow will typically be used in the following way. dm-bow will be loaded with a
39 switched to state 1. The file system will now be used as normal. At some point,
40 the changes can either be committed by switching to state 2, or rolled back by
41 unmounting the file system, removing the dm-bow device and running the command
42 line utility. Note that rebooting the device will be equivalent to unmounting
57 SECTOR0 is the first sector on the device, and is used to hold the log of
61 writes from the true sector zero are redirected to. Note that like any backup
62 sector, if the sector is written to directly, it must be moved again.
65 Thus if it is written to or trimmed, the contents must first be backed up.
68 to or used for backup. On being written to, a FREE sector is changed to CHANGED.
74 to, the contents must first be backed up again.
76 All backup operations are logged to the first sector. The log sector has the
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93 and potentially limits the time spent trying to restore a corrupted snapshot.
98 log entry to be written.