mirror without destroying existing contents
lists at jnielsen.net
Tue Mar 13 19:42:06 UTC 2007
On Tuesday 13 March 2007 15:12, Steve Franks wrote:
> Anyone made a mirror w/o destroying what's in the disk already? The
> atacontrol man page is less than adequate in this respect...is is even
If you want to use gmirror (which I recommend), the most conservative approach
is as follows. This can probably be adapted to other mirroring
techniques/software as well.
Verify that your backups are up-to-date and reliable.
Create a "degraded" single-member mirror on the blank disk (or a
partition/slice on said disk). (gmirror label command) Make sure that the
size of the disk/slice/partition is equal to or smaller than the size of the
disk/slice/partition which already contains your data.
Create (a) new filsystem(s) on the new mirror. (newfs and possibly bsdlabel,
depending on how/if you want to break it up)
Transfer your data from the existing filesystem to the new filesystem
(dump/restore -- it's easier than it sounds). (Alternative: restore from the
backup you created to begin with.)
Verify data transfer, make relevant changes to /etc/fstab, possibly other
Destroy the original filesystem (possibly using dd and /dev/zero) (not
strictly necessary, but wiping at least the first part of the
disk/slice/partition can help avoid potential confusion (for you and the
Insert the original disk/slice/partition into your new mirro (gmirror insert
This approach can take longer than some others (due to the transfer
requirement), but the finished product is less likely to contain surprises. I
have successfully used this approach to migrate several types of volumes to
gmirror sets, including boot partitions.
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