About /etc/fstab and LABELs

[Kostas Sfakiotakis]

Ed Wilts wrote:

>On Fri, Oct 07, 2005 at 12:57:03AM +0300, Kostas Sfakiotakis wrote:
>  
>
>>Ed Wilts wrote:
>>
>>    
>>
>>>Labels can save you from MAJOR problems in a lot of specific situations.
>>>Imagine that you have 3 disks, sda, sdb, and sdc.  Now imagine that sdb
>>>fails hard.  
>>>
>>>      
>>>
>>Well the problem is that sdb failled and the DATA whatever
>>they were are gone !!! and certainly there is no label trick
>>that is going to save someone from that .
>>    
>>
>
>No, but you should not lose other data because of it. 
>

I don't know if you agree with me on that but backups do serve
on that purpose . A nice backup will help on the direction of not
loosing data or in the worst occassion minimize the loss .

> Predictability in  system configurations is what keeps us employed. 
>
>  
>
>>>You reboot and what was sdc is now sdb.  You will mount
>>>that filesystem on the wrong mount point and suddenly cause yourself all
>>>sorts of grief and possible disk corruption depending on how well
>>>behaved your applications are.  Imagine that sdb was your backup drive
>>>and you did an rsync --delete from sda to sdb automatically via cron or
>>>in rc.local.  Kiss all the data that was on sdc goodbye
>>>
>>>      
>>>
>>Well i thought there was a Rescue mode in Linux . Since there is
>>a disaster rescue mode can be used to edit the scripts so they
>>reflect the current situation .
>>    
>>
>
>You're assuming you caught the issue in time.  What if your swap file
>was on sdb?  Your system will likely crash, it will hopefully come up
>but sdc becomes sdb.  You may come up without swap.
>  
>

You caught me there , i don't know what happens if a system
tries to boot without a swap partition.  In case there is enough
memory available it might boot in case there is not enough memory
though ...... it is pretty possible that it will crash . Now as far as the
damage is concerned i guess it depends on what filesystems were
mounted at that point and what was going on at the point of the crash ...

>The whole point is to make sure that the system actions are predictable
>- what is sdc today will always be sdc - the mount point follows the
>physical disk.
>  
>
In that perspective i can't say that things work otherwise .
In another point of view i would try though to the best of
my ability not to loose DATA no matter what happens .

>The same problem came occur if you add a drive - there's no guarantee
>that your system will scan the drives in the same order when you come
>up after the drive install.
>
>  
>
Since you are focusing on the sd* notation i guess you are
focusing to what happens on a SCSI controller , on the other
hand IDE controllers are tottaly independent from that problem

For example /dev/hdc will always refer to the Secondary Master
no matter if it is the only device or if there are 3 or more devices
connected to the computer ( I used to run Redhat 7.3 on a computer
with a PDC 20267 controller with a total of 4 disks a cdrecorder and
a cd drive and i never had a problem .

Besides  answer me this : Let's assume that on one box you have
Redhat 7.3 but because it is out of date you want to install on the
same box  Fedora Core 4 for example ( Dual boot with 2 Linux
versions ) . If you use labels for the root device , then on boot
how will the Redhat 7.3 know which is it's root partition so it will
try to boot from there and which is the Fedora Core 4 ( btw a
2.6.* kernel and NOT a 2.4 ) so it will not use it ???


All am trying to say here is . There are certainly occassion where
LABELS will make things easier , that's the reason they were
originally created , but there are also occassion where LABELS
will not be as helpfull . Now whether you use labels or not  is
dependent to what you want to accomplish with the hardware and
software combination that you have . Should labels make things easier
then by all means go ahead and use them , should they not then don't
use them .  In my opinion there is no single one trick
( be it labels or whatever ) that will always be there for you when
things start to fall apart .

Kind Regards,
   Kostas