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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 dca274ff400..a5009c8300f 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.
*) snapshot-origin <origin>
which will normally have one or more snapshots based on it.
-You must create the snapshot-origin device before you can create snapshots.
Reads will be mapped directly to the backing device. For each write, the
original data will be saved in the <COW device> of each snapshot to keep
its 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.
*) snapshot <origin> <COW device> <persistent?> <chunksize>
-A snapshot is created of the <origin> block device. Changed chunks of
+A snapshot of the <origin> block device is created. Changed chunks of
<chunksize> sectors will be stored on the <COW device>. Writes will
only go to the <COW device>. Reads will come from the <COW device> or
from <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.
<persistent?> is P (Persistent) or N (Not persistent - will not survive
after reboot).
+The difference is that for transient snapshots less metadata must be
+saved on disk - they can be kept in memory by the kernel.
How this is used by LVM2