[lug] SW Raid question

[Hugh Brown]

On Tue, 24 Jul 2007 dio2002 at indra.com wrote:

>
> > 2.5) Get another cheap SATA non-RAID card and replace the on-board with
> > this.
>
> One other question related to this.
>
> Lets say i go ahead and enable the compatability mode right now so i can
> install my sw raid / lvm setup and get up and running.  Lesser performance
> isn't going to kill me right now.
>
> If i buy a SATA card as you describe for install at some point in the near
> future, i should be able to install the card, plug in my old drives and
> the system should boot / run with them without a reinstall right?  the way
> i understand it is that sw raid should be hw independent (after all it's
> implemented in sw)?
>
> Of course this assumes that i don't need to compile a driver for the card.
>
> But even if i did, I imagine i could mkinitrd with the new driver module,
> install my new initrd in /boot and grub install BEFORE installing the new
> sata card so kernel finds what it needs on reboot?
>
>


You'd need the SATA card to be supported and you'd need to plug the drives
in with the same ordering.

Re: grub
I don't remember if I had time to test this (short downtime), but these
are the notes I had (borrowing from
http://deb.riseup.net/storage/software-raid/)

----------------------------------
grub> find /grub/stage1

# should spit out (hd0,0) (hd1,0)

Grub>device (hd0) /dev/sdb (/dev/hdb for ide)
Grub>root (hd0,0) and then:
Grub>setup (hd0)

# Notice that we made the second drive device 0.  Why is that you ask?
Because device 0 is going to be the one with mbr on the drive so passing
these commands to grub temporarily puts the 2nd mirror drive as 0 and will
put a bootable mbr on the drive and when you quit grub you still have the
original mbr on sda and will still boot to it till it is missing from the
system.

If your first disk fails, however, your second disk will then be the first
disk in the system, and so the MBR will be correct.

---------------------------------------------

I had scsi disks on sda and sdb in the example above.

FWIW,

Hugh