Nico Kadel-Garcia wrote:
> Hi, folks. I'm looking at taking a software repository of some 200 Gigabytes
> that lives on a Terabyte RAID array and creating LVM snapshots in order to
> be able to backup the snapshot, not the active file system, and avoid some
> of the "files changing while doing backup" problems I'm having with the
> Amanda setup. But I have some related questions.
>
> 1: How long does the snapshot process take, typically? Since I'll need to
> freeze the main filesystem to get a good snapshot, I don't want to freeze it
> for too long, or the people who need the data will get upset.
>
> 2: Which kernel should I be using? I'm seeing various notes about
> file-system locking features that may or may not be supported in specific OS
> releases: I'm comfortable with RedHat and its variants, so I'd be
> comfortable using Centos 4 or Fedora Core 2 or better, but will I need to
> rebuild my kernel with added options and prevent auto-updates of my kernels
> to avoid losing important locking features?
>
> 3: What filesystem best supports this? I see notes about people using ext3
> and JFS for this stunt, but am not sure what is best for this application.
> Good performance under heavy I/O is critical for what I'm doing.
>
>
You really need to google around on this, I forget the details because I
didn't need them, but it takes no time, a flag is set and changes
(writes) are set aside, or journaled, or similar, and the original copy
can be read.

I read about this a while ago and don't remember the details, but
similar capabilities on other systems work that way, you need to do the
reasearch. It isn't done by locking, it's at a lower level.

--
bill davidsen
SBC/Prodigy Yorktown Heights NY data center
http://newsgroups.news.prodigy.com