|
Re: LVM snapshots
2006-07-07 14:53:38
--On July 7, 2006 2:35:23 AM -0700 "Joe Donner (sent by Nabble.com)"
<lists AT nabble DOT com> wrote:
Does anyone use or have knowledge of using LVM snapshots with Amanda
backups?
I believe it to be the same concept as Shadow Volume Copies in Windows
2003, and that is quite useful.
A little bit of info here:
http://arstechnica.com/articles/columns/linux/linux-20041013.ars
I'm just wondering what happens during the freeze - how freezing "all
activity to and from the filesystem to reduce the risk of problems"
affects the system? One would imagine that disk writes are somehow
queued up and complete when the file system is unfreezed again?
It's only stopped long enough to make the bitmap table. After that it's
Copy On Write. Meaning a snapshot is free until the 'original' starts to
differ then the snapshot starts to take up space because you have to make
copies of the original blocks for the snapshot once they start to change.
In 2.4 atleast though LVM snapshots are extremely limited. The kernel has
to find a contiguous section of RAM to put the bitmap table of COW pages
in. If you've a significantly sized LVM LV you won't be able to snapshot
it even reliably.
A better place to ask how does LVM work would be one of the LVM discussion
groups.
Here's a couple helpful links.
<http://tldp.org/HOWTO/LVM-HOWTO/lvm2faq.html>
<http://www.tldp.org/HOWTO/LVM-HOWTO/>
Joe
--
View this message in context:
http://www.nabble.com/LVM-snapshots-tf1905387.html#a5214340 Sent from the
Amanda - Users forum at Nabble.com.
--
"Genius might be described as a supreme capacity for getting its possessors
into trouble of all kinds."
-- Samuel Butler
|
|
|
