[linux-lvm] Q: LVM over RAID, or plain disks? A:"Yes" = best of both worlds?

[hansbkk at gmail.com]

On Tue, Nov 30, 2010 at 10:41 PM, Andrew Gideon <ag2827189 at tagmall.com> wrote:
> I'm having some difficulty following this thread, so perhaps I've missed
> some other aspect to this.  But the above makes it seem like you simply
> wish to transport snapshots.  Why not use something as straightforward as
> dd for this rather than RAID1?  RAID1 tools (mdadm, drbd, etc.) have the
> benefit of keeping volumes in sync over time.  But the above process
> describes a synchronization over a single instant (the instant of the
> snapshot being taken).  So why bother with the extra work/capability/
> complexity?

Our posts must have crossed in the mail - please see my message
immediately prior to this one.

> I'm also puzzled by something you wrote in your very first message on
> this thread: "the hard-linked filesystems on FILER-B require full
> filesystem cloning with block-level tools rather than file-level copying
> or sync'ing."  Why?  rsync -H handles cloning of hard links (though at a
> performance cost).

The performance cost becomes unworkable when you are talking about a
filesystem with literally millions of hardlinks, as any reasonably
well-used rsnapshot/rdiff-backup/BackupPC installation will create.
Perhaps my current problem will be overcome by adding 64GB of RAM to
my host, but as the number of hardlinks grows. . .

It is precisely this problem I'm trying to address.
http://www.google.co.th/search?hl=en&q=backuppc+pool+rsync+hard-link