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-rw-r--r--Documentation/device-mapper/snapshot.txt5
1 files changed, 3 insertions, 2 deletions
diff --git a/Documentation/device-mapper/snapshot.txt b/Documentation/device-mapper/snapshot.txt
index dca274ff4005..a5009c8300f3 100644
--- a/Documentation/device-mapper/snapshot.txt
+++ b/Documentation/device-mapper/snapshot.txt
@@ -19,7 +19,6 @@ There are two dm targets available: snapshot and snapshot-origin.
19*) snapshot-origin <origin> 19*) snapshot-origin <origin>
20 20
21which will normally have one or more snapshots based on it. 21which will normally have one or more snapshots based on it.
22You must create the snapshot-origin device before you can create snapshots.
23Reads will be mapped directly to the backing device. For each write, the 22Reads will be mapped directly to the backing device. For each write, the
24original data will be saved in the <COW device> of each snapshot to keep 23original data will be saved in the <COW device> of each snapshot to keep
25its visible content unchanged, at least until the <COW device> fills up. 24its visible content unchanged, at least until the <COW device> fills up.
@@ -27,7 +26,7 @@ its visible content unchanged, at least until the <COW device> fills up.
27 26
28*) snapshot <origin> <COW device> <persistent?> <chunksize> 27*) snapshot <origin> <COW device> <persistent?> <chunksize>
29 28
30A snapshot is created of the <origin> block device. Changed chunks of 29A snapshot of the <origin> block device is created. Changed chunks of
31<chunksize> sectors will be stored on the <COW device>. Writes will 30<chunksize> sectors will be stored on the <COW device>. Writes will
32only go to the <COW device>. Reads will come from the <COW device> or 31only go to the <COW device>. Reads will come from the <COW device> or
33from <origin> for unchanged data. <COW device> will often be 32from <origin> for unchanged data. <COW device> will often be
@@ -37,6 +36,8 @@ the amount of free space and expand the <COW device> before it fills up.
37 36
38<persistent?> is P (Persistent) or N (Not persistent - will not survive 37<persistent?> is P (Persistent) or N (Not persistent - will not survive
39after reboot). 38after reboot).
39The difference is that for transient snapshots less metadata must be
40saved on disk - they can be kept in memory by the kernel.
40 41
41 42
42How this is used by LVM2 43How this is used by LVM2