[linux-lvm] snapshots documentation clarification

[Dane Miller <dane@greatschools.net>]

afternoon collector
	lvm reading
	GS update: single auth db
	check ebay

	bmi virtual machine
	zimbra schedule downtime: snapshot conversion
	zimbra security updates

Hi,

Section 3.8 "Snapshots" of the LVM Howto has a scary warning after the first paragraph (http://tldp.org/HOWTO/LVM-HOWTO/snapshotintro.html), with a caveat in the last sentence:
  "If the snapshot size equals the origin size, it will never overflow."

What exactly does this mean?  Does this imply that it's safe to use "long-term" snapshots whose size is equal to the origin's size, without worrying about effects of significant divergence from the original?  Long-term to me is 3yrs as the root fs of a (Xen domU) mail server.

Note that in this case, writes to the root fs will be limited to logs (/var/log) and software updates.  Mailboxes live on a separate, non-snapshot logical volume.

Thanks,

Dane