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#1 (**permalink**) 01-18-2008, 08:11 AM

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.

#2 (**permalink**) 01-18-2008, 08:13 AM

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

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New mirror snapshot LVM setup planned, what do I need