I was setting up a machine to handle some of our backups at work. It's not a critical system, so instead of setting up a RAID across 3 250GB drives, I just set up LVM so I could take advantage of all 750GB. This were going along fine, but then I wanted to see what the status of LVM was...So I ran 'lvdisplay' and got this very disturbing message:

Couldn't find device with uuid 'tcRo2m-XJ1W-JFUh-FuYP-dbbW-RHSx-FFnQ4r'.

Couldn't find all physical volumes for volume group ide_drives.

Couldn't find device with uuid 'tcRo2m-XJ1W-JFUh-FuYP-dbbW-RHSx-FFnQ4r'.

Couldn't find all physical volumes for volume group ide_drives.

Volume group "ide_drives" not found

Uh oh...Did one of the drives fail already? 'pvscan', etc. didn't yield any better results.

But then I notice the device that isn't found is '/dev/hdb', which does have the correct uuid. But it also happens that '/dev/cdrom' is a symlink to '/dev/hdb', so lvm was ignoring that device because it thought it was a cdrom device! AAARGH. Only took me 2 hours to figure that one out. I'm hoping this post can save somebody else some time.

On that same machine, I wanted to set up rsync to handle the backups since it's well suited for that purpose. I had just discovered rsync's filter rule syntax so I wanted to play around with that to specify which directories on which machines should be backed up. Lets say my directory structure looks like this:

/

/etc

/home -> /mnt/raid/home

/mnt

/mnt/raid/

/mnt/raid/home

/proc

/tmp

...

and I want to back up both /etc and /home. So I tried this set of rsync filter rules:

• /etc/

• /etc/**

• /home/

• /home/**

• *

No luck at all. rsync refused to copy over the home directories.

Again, several hours were lost figuring this out. I think what was happening was that rsync was happily copying the /home symlink and not looking deeper into the directory structure. So when it came to the '- *' rule, the actual home directories were being excluded. I solved this by adding

• /mnt/

• /mnt/raid/

• /mnt/raid/home/

• /mnt/raid/home/**

to my filter rules instead of the '/home' stuff.