Eric Anderson wrote:
Mike Jakubik wrote:
Craig Boston wrote:
On Tue, Mar 07, 2006 at 09:04:02AM -0800, Freddie Cash wrote:
There's no need to copy files around. gmirror handles it all for you
behind the scenes. Just create the gmirror labels using the existing
disks/slices/partitions, then insert the second set of
disks/slices/parittions. gmirror will handle synchonising the data
across the mirror.
AFAIK, gmirror causes whatever provider it's mirroring to "lose" the
last block to metadata. I've always avoided mirroring an existing
filesystem for fear that shrinking a UFS filesystem's underlying device
might cause problems down the road.
Can someone with knowledge of the UFS internals please confirm one way
or the other if this is dangerous or not?
I'm curious to know this as well, as i have some systems using
gmirror, that were setup in this fashion. Could someone knowledgeable
on the matter shed some light?
I've gmirrored existing disks/slices before, and it's worked fine.
I'm not 100% certain about all cases, but it's possible that the
filesystem could be right up against the last block of the partition,
and it could get stomped on I suppose.
I'm not sure what this command tells you for sure, but it dumps the
last block of a slice, or disk, or whatever:
dd if=/dev/ad0s3a iseek=`diskinfo ad0s3a | perl -ne '@d = split; print
($d[2]/$d[1] - 1)'` count=512 | hexdump
Could someone provide an authoritative answer to this please? Pawel, it
would be nice to see some support for your own code from you. This is a
very easy method to create a mirror on an existing system, but if its
going to cause problems then its useless (All the more reason for geom
enabled installer).
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