[CentOS] add on sata card relabeling drives, installation

Fri Sep 30 19:36:50 UTC 2011
Bob Hoffman <bob at bobhoffman.com>

Well, first thing is I got lucky and not bought all the same drives. If 
I had all the same I would never have known I put my OS on the two 
drives added with the new sata card, something I DID NOT want to do.

If they were all 1 tb drives, it would have been a disaster to me. 
Luckily I set up P0-P2 drives with my 500gb and saw the issue immediately.

Below is the issue I am talking about. The system ignores the sda/sdb
etc labeling to use UUID and things like hd0, hd1...
Yet mdstat shows you the drives in the useless labeling way...sda sdab

lamar owen wrote
There seem to be enough differences in the md scheme of 5.x and 6.x to 
discourage disk interchange among the two in mdraid cases.  Having said 
that, I have an EL6.1 (upstream EL) machine with this:
[root at www ~]# cat /proc/mdstat
Personalities : [raid1]
md127 : active raid1 sdae1[0] sdaf1[1]
       732570841 blocks super 1.2 [2/2] [UU]

taking out a dead drive and adding a new one negates a real ability to 
re-label them as you want since the new drive would have a different 
UUID/serial, etc..and screw up any label system you might have done.

That mdstat is not the only monitoring software that pays attention to 
the 'useless' labels like sda sdb sdc, etc...

and that leads to my fear of not getting accurate reports on problems 
with drives or partitions...

(in my case I have 8 drives with 2 raid1 arrays made up of 3 drives 
each, each one having a hot spare....and then a few drives as backups)

I am going to just leave it alone, but I feel their is something missing 
in the whole theory...
if the labels sda, sdb, etc mean nothing to the system admin, then why 
are they used in monitoring software...and worse, why are they the only 
drive identification listed in the installer???

And the disk manager, graphical one, in centos 6 does not list the UUID, 
it calls it 'worldwide ID'.

By forcing the use of UUID it makes monitoring impossible. If your 
scripts use the UUID, then you must know the UUID and add them manually. 
If you change out a drive, your script now fails to pick up the new 
UUID....very annoying.

I am sure it is needed, but I still see UDEV using unchanging labeling 
(things I would use to add grub on a drive) like 'HD0,HD1, etc.

why even use the labels, just use HD1, HD2 and the UUID and let it be.