Replacing disk in Linux Software RAID 1

Michael Mansour micoots at yahoo.com
Wed Aug 18 13:58:52 UTC 2004


Hi,

 --- jludwig <wralphie at comcast.net> wrote: 
> On Tue, 2004-08-17 at 11:26, Robin Laing wrote:
> > Michael Mansour wrote:
> > > Hi Robin,
> > > 
> > > Yahoo truncated most of the email so I'll just
> try to
> > > answer your specific question.
> > > 
> > > 
> > >>Would it be possible to write the MBR to the
> second
> > >>disk just in case?
> > >>-- 
> > >>Robin Laing
> > > 
> > > 
> > > Yes, I've tested this by removing the first
> drive and
> > > writing grub to the MBR of the second drive and
> it did
> > > work fine, although when putting the first drive
> back
> > > in there then I had the issue with two MBR's
> which got
> > > things a little confused.
> > > 
> > > Basically, what I learnt from that saga is that
> grub
> > > should only reside on one drive.
> > > 
> > > Michael.
> > > 
> > > 
> > > Find local movie times and trailers on Yahoo!
> Movies.
> > > http://au.movies.yahoo.com
> > > 
> > > 
> > 
> > This is interesting.
> > 
> > I don't use RAID for my system drives but I do for
> /home so it isn't 
> > an issue for me.  But in a production system, it
> would be very 
> > convenient to have the MBR on both drives in case
> the boot drive does 
> > fail.  Move the second drive and then you can
> reboot.
> > 
> > I for one when I was a system admin, did not like
> getting called in at 
> > 03:00 due to a crash.  And doesn't always seem to
> happen at 03:00 when 
> > things go bad?  :)
> > 
> > I feel it should be there.  Now if you do write it
> to the second disk 
> > and you have problems, this could be a problem.
> > 
> > -- 
> > Robin Laing
> Many newer BIOS' will allow for booting off of a
> secondary drive.
> 
> If this is the case with your machine I would just
> load the second drive
> where it sits and just change the BIOS setting if
> necessary.
> 
> (I used to do this with SCSI and IDE for a duel boot
> system.)

Yeah, I've tested this both with and without that
feature in the BIOS and it works fine as long as grub
is on the MBR. With a server I've tested which doesn't
have that feature, I simply added an Adaptec 1200A
raid controller (though the hardware raid function is
_not_ enabled on it), and in that controllers setup
screen you can choose which drive to boot from by
selecting it from its menus.

Either way works fine, but as someone else suggested
in this thread, grub has limitations to writing it's
MBR to both drives (lilo doesn't seem to have a
problem with that though). IMHO this is a major
problem with grub and when I had the last issue with
the server it almost prompted me to buy a 3ware
controller and abandon software raid altogether. The
next server I buy to replace this one will be one with
a 3ware card in it, for now I wouldn't bother wasting
2 weeks rebuilding a production server, might as well
wait till FC3 is out and go for it then with hardware
raid.

Michael.


Find local movie times and trailers on Yahoo! Movies.
http://au.movies.yahoo.com





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