From 411f11405c99141233970c98d23d6a5ec88a4f7f Mon Sep 17 00:00:00 2001 From: Paolo 'Blaisorblade' Giarrusso <blaisorblade@yahoo.it> Date: Mon, 7 Nov 2005 01:01:01 -0800 Subject: [PATCH] [PATCH] Fix dm-snapshot tutorial in Documentation I've recently added this documentation, Alasdair gave some corrections, and here are some further corrections on top of his work (partly style issue, partly a technical error due to different past experience, partly a note which I've added - i.e. transient snapshots are lighter). Cc: Alasdair G Kergon <agk@redhat.com> Signed-off-by: Paolo 'Blaisorblade' Giarrusso <blaisorblade@yahoo.it> Signed-off-by: Andrew Morton <akpm@osdl.org> Signed-off-by: Linus Torvalds <torvalds@osdl.org> --- Documentation/device-mapper/snapshot.txt | 5 +++-- 1 file changed, 3 insertions(+), 2 deletions(-) diff --git a/Documentation/device-mapper/snapshot.txt b/Documentation/device-mapper/snapshot.txt index dca274ff40052..a5009c8300f33 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 -- GitLab