A curse on LABEL=

[Bob Marcan]

Timothy Murphy wrote:
> Bryan O'Sullivan wrote:
> 
> 
>>>How exactly would adding a new DVD drive stop the computer booting?
>>
>>You open your computer.  You pop the DVD drive in.  Cables don't reach,
>>so you move some around.  Your boot drive now has a different device
>>number under Linux which, if you're not using something like LABEL in
>>/etc/fstab, will render your machine unable to boot.
> 
> 
> I find this scenario slightly bizarre.
> First of all, I wouldn't expect my computer to boot at all
> if I changed the disk controllers around,
> whether I was using LABELs or not.
> (I would start by using tomsrtbt or Knoppix
> to see where the machine thought the disks were.)
> I'm not sure what would happen on my rather ancient machine
> if I moved the cables so my DVD was /dev/hda.
> And my computer at least will only boot from /dev/hda or /dev/hdb,
> so the changes I could make are rather limited.
> 
> As this probably makes clear, I am no computer guru.
> But I've read dozens of queries over the years
> from people who have been caught out by LABELs,
> while I don't recall anyone complaining that they changed round
> the controller connections inside the computer
> and this caused the machine to cease to boot.
> Wouldn't it immediately occur to anyone sufficiently au fait
> with the inside of a computer to change the connections around
> that they would have to consider their setup rather carefully?
> Eg I imagine this would cause chaos on most Windows systems,
> if C: suddenly became E: or whatever.
> 
> I honestly expected to be shown simple, likely to occur, scenarios
> where LABELs are helpful,
> but all the examples that have been suggested
> are ones I cannot imagine a non-guru like me ever encountering.
> 
> 

This is how is it done on the Tru64.

gin$ sudo scu show edt

CAM Equipment Device Table (EDT) Information:

     Bus/Target/Lun Device Type  ANSI  Vendor ID    Product ID 
Revision N/W
     -------------- ----------- ------ --------- ---------------- 
-------- ---
      4    3    0   Sequential  SCSI-2 HP        HP35470A          1109 N
      5    0    0   Direct      SCSI-2 WDC WD80  0BB-00CAA1        17.0 W
      5    1    0   Direct      SCSI-2 WDC WD80  0BB-00CAA1        17.0 W
      6    0    0   Direct      SCSI-3 COMPAQPC  ATLAS 10K 9 WLS   UCJ5 W
      7    5    0   CD-ROM      SCSI-2 IBM       CDRM00203         BZ26 N

gin$ sudo hwmgr show scsi

         SCSI                DEVICE    DEVICE  DRIVER NUM  DEVICE FIRST
  HWID:  DEVICEID HOSTNAME   TYPE      SUBTYPE OWNER  PATH FILE   VALID PATH
-------------------------------------------------------------------------
    91:  8        gin        disk      none    2      1    dsk11  [5/0/0]
    92:  9        gin        disk      none    2      1    dsk12  [5/1/0]
    93:  10       gin        disk      none    2      1    dsk13  [6/0/0]
    94:  11       gin        cdrom     none    0      1    cdrom0 [7/5/0]
   128:  0        gin        tape      none    0      1    tape0  [4/3/0]
gin$

dsk11 is allways dsk11 wherever inserted.
11 in dsk11 is only the sequence number.
Names are not reused, but they can be changed, swaped, deleted ...
dsk0 thru dsk10 are installed in the separate box and currently not 
connected. It doesn't matter to which controller are connected, they 
will retain the same device file.
No writting to the platter. It is computed from the info on the disk: 
disk type, serial number ... Don't know exactly.
I have some warnings at the boot with disk12 and 13, which are WD 80 GB 
IDE connected thru the Acard scsi to ide adapter, but this is a special 
case.

LABEL= is a good approximation to this.

Regards, Bob
-- 
  Bob Marcan                     mailto:bob.marcan at hermes-plus.si
  Aster^H^H...HermesPlus^H^H^H...S&T
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