SATA internal disk and external drive - device changes

[Derek Broughton]

Rashkae wrote:

> Ed Jabbour wrote:
>> Internal SATA drive designated as sdax.  I attached an external hard
>> drive
>> enclosure via USB.  Instantly recognized as sdb.  I formatted the
>> external
>> and successfully transferred files back and forth.  However, on a reboot
>> with the external left on, I have the internal as sdbx and the external
>> as sdc and
>> sdc1.  Turned the external off and rebooted and I get sda and sdb.  Any
>> advice, hints, pointers, etc. appreciated.  Relevant fstab entry:
>> 
>> /dev/sdb1 /mnt/external ext3 user,atime,noauto,rw,nodev,noexec,nosuid 0 0
>> 
> 
> These are the kinds of reasons why Ubuntu now uses the UUID syntax in
> the fstab file.  Modern Bioses can re-organize the order of hard drives
> every which way, and Linux, by design, will change drive designations
> depending on which drivers get loaded first.  You need to identify what
> the UUID of your partitions are, then put that in your fstab file
> instead of /dev/sdb1 (and all your other drives as well)

This is the first example I've seen where UUID is really necessary, but I
agree it's the solution.  One caveat - I've got the impression that not all
filesystems support UUID yet.  I could be wrong about that, but you'd want
to be sure ahead of time - easy enough to check, just don't reboot without
making sure everything in your /etc/fstab will remount smoothly.

>> Lastly, the external is one partition; I thought so, anyway.  Why sdb and
>> sdb1?  sdb won't mount - wrong fs type, bad superblock stuff.  Did not
>> format correctly?
>> 
> 
> yes, you formatted your drive correctly. sdb gives direct access to your
> whole drive, sdb1 is access to the first (and in this case, only
> partition) on this drive.  I wonder if it's possible in linux to create
> a filesystem directly on a drive without any partitions? 

???  It seems to me that I have had a working USB stick with the entire
device formatted directly.  It caused no end of headaches!

> Even if it 
> would work, I'm not sure there would be any advantage to doing something
> like that.  However, suppose you had multiple partitions, sdb1, sdb2,
> sdb5, etc.  you could, if you wanted, erase everything on the hard
> drive, including the partition table, with a command like dd
> if=/dev/zero of=/dev/sdb 

I think the mere fact that you can do that is evidence that you _could_ have
an fs formatted directly on the device, but so much expects a drive to
be /dev/[hs]dX and its partitions to be /dev/[hs]dXN, that it wouldn't be
worth the trouble.
-- 
derek