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[linux-lvm] re --corelog: does synchronization re-copy all data?

In the LVM Administrator's Guide, at least the one at
http://www.centos.org/docs/5/html/Cluster_Logical_Volume_Manager/LV_create.html ,
it says:"

  LVM maintains a small log which it uses to keep track of which regions
  are in sync with the mirror or mirrors. By default, this log is kept
  on disk, which keeps it persistent across reboots. You can specify
  instead that this log be kept in memory with the --corelog argument;
  this eliminates the need for an extra log device, but it requires that
  the entire mirror be resynchronized at every reboot.

Does that last sentence mean that _all_ the data is recopied, or just
that all _regions_ are checked and not all the data necessarily has
to be copied (perhaps only change regions have to be copied, but
unchanged regions don't)?

More generally, can LVM perform RAID1-style mirroring with only
two disks (without having to re-copy everything each boot)
(and, of course, being recoverable in case either disk fails)?

Daniel B.
dsb smart net

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