Question on MBR of SATA Raid 1 Software

[Dario Lesca]

I have install my fc6 server with RAID-1 software on 2 SATA HD.
All work fine.

My question is:

If HD1 crash, HD2 is ready for boot the system? I have see witch the MBR
of the 2 disk is different. (see follow explanation)...

I must copy with this command:

# dd bs=512 count=1 if=/dev/sda of=/dev/sdb

MBR of first disk on MBR of second disk?

Or this operation is not necessary?

Many thanks!
> [root@s-scarwall ~]# dd bs=512 count=1 if=/dev/sda of=/tmp/sda 
> 1+0 records in
> 1+0 records out
> 512 bytes (512 B) copied, 0,0119784 seconds, 42,7 kB/s
> [root@s-scarwall ~]# dd bs=512 count=1 if=/dev/sdb of=/tmp/sdb
> 1+0 records in
> 1+0 records out
> 512 bytes (512 B) copied, 0,0175179 seconds, 29,2 kB/s
> [root@s-scarwall ~]# diff /tmp/sd?
> Binary files /tmp/sda and /tmp/sdb differ
> [root@s-scarwall ~]# hexdump -C /tmp/sda>/tmp/sda.txt
> [root@s-scarwall ~]# hexdump -C /tmp/sdb>/tmp/sdb.txt
> [root@s-scarwall ~]# diff /tmp/sd?.txt
> 5c5
> < 00000040  80 00 00 80 41 24 02 00  00 08 fa 90 90 f6 c2 80  |....A$..........|
> > 00000040  81 00 00 80 41 24 02 00  00 08 fa 90 90 f6 c2 80  |....A$..........|
>
> 28c28
> < 000001b0  00 00 00 00 00 00 00 00  21 d0 00 00 00 00 80 01  |........!.......|
> > 000001b0  00 00 00 00 00 00 00 00  bf 7e 08 00 00 00 80 01  |.........~......|
>
> [root@s-scarwall ~]#

[Bruno Wolff III]

On Fri, Mar 02, 2007 at 14:30:51 +0100,
  Dario Lesca  wrote:
> I have install my fc6 server with RAID-1 software on 2 SATA HD.
> All work fine.
>
> My question is:
>
> If HD1 crash, HD2 is ready for boot the system? I have see witch the MBR
> of the 2 disk is different. (see follow explanation)...
>
> I must copy with this command:
>
> # dd bs=512 count=1 if=/dev/sda of=/dev/sdb
>
> MBR of first disk on MBR of second disk?
>
> Or this operation is not necessary?

Currently grub is not software raid aware and the default is to only install
it on one of the mirrors. You want to manually install it on the other
drive as well, but when you do it should be set up to install from hd0, not
hd1 (even though it is being put on hd1) because most likely after a drive
failure hd1 will been seen as hd0. Unfortunately grub doesn't seem to
have a way to say install off the current drive no matter what drive number
it is.
grub2 is going to have some ability to use software raid, but the last time
I checked it, it didn't work.

[Dario Lesca]

Il giorno ven, 02/03/2007 alle 10.45 -0600, Bruno Wolff III ha scritto:
> Currently grub is not software raid aware and the default is to only
> install
> it on one of the mirrors. You want to manually install ....

Then I must copy the MBR of first disk on MBR of second disk? or not?

[ ] Yes, all people after a RAID install must do that, otherwise
    if the first disk crash the system it does not start.
[ ] No, only you have this issue, if you remove the
    first disc all work fine

Please, check the right answer.

Many thanks!

[Bruno Wolff III]

On Wed, Mar 07, 2007 at 23:53:45 +0100,
  Dario Lesca  wrote:
> Il giorno ven, 02/03/2007 alle 10.45 -0600, Bruno Wolff III ha scritto:
> > Currently grub is not software raid aware and the default is to only
> > install
> > it on one of the mirrors. You want to manually install ....
>
> Then I must copy the MBR of first disk on MBR of second disk? or not?
>
> [X] Yes, all people after a RAID install must do that, otherwise
>     if the first disk crash the system it does not start.
> [ ] No, only you have this issue, if you remove the
>     first disc all work fine
>
> Please, check the right answer.
>
> Many thanks!

I am not sure that everything you need is on the MBR, but for sure if you
do nothing only one disk in the array will get grub installed in the MBR
without taking further action.
This only applies to RAID 1 on the boot partition. Other types of RAID or LVM
can't be used on that partition, if you want your system to boot.

[David Fletcher]

On Friday 02 March 2007 13:30, Dario Lesca wrote:
> I have install my fc6 server with RAID-1 software on 2 SATA HD.
> All work fine.
>
> My question is:
>
> If HD1 crash, HD2 is ready for boot the system? I have see witch the MBR
> of the 2 disk is different. (see follow explanation)...

This is also of interest to me, because I'm hoping to be ordering one of 
these:-

http://linitx.com/product_info.php?products_id=1083

sometime in the next few days, for building a low power mini server for home 
use.

It has two SATA connectors and the data states that it can do RAID 0 and 1. 
Question is, is it likely to be a proper hardware raid on this board or will 
it have to be software RAID like the OP has installed?

Dave F

[Bruno Wolff III]

On Fri, Mar 02, 2007 at 17:36:10 +0000,
  David Fletcher  wrote:
> It has two SATA connectors and the data states that it can do RAID 0 and 1. 
> Question is, is it likely to be a proper hardware raid on this board or will 
> it have to be software RAID like the OP has installed?

If it is a cheap raid controller without battery backed cache, you probably
don't want to have it doing raid, just use the software raid (not dmraid)
instead. It may be faster and you won't be tied to specific hardware.

[Justin Zygmont]

On Fri, 2 Mar 2007, Dario Lesca wrote:
> I have install my fc6 server with RAID-1 software on 2 SATA HD.
> All work fine.
>
> My question is:
>
> If HD1 crash, HD2 is ready for boot the system? I have see witch the MBR
> of the 2 disk is different. (see follow explanation)...
>
> I must copy with this command:
>
> # dd bs=512 count=1 if=/dev/sda of=/dev/sdb
>
> MBR of first disk on MBR of second disk?
>
> Or this operation is not necessary?
>
> Many thanks!

hi, what I did about this, was to install grub on the second HD:

root (hd1,x)
find /boot/grub/stage1
setup (hd1)

Hope this helps..

[Bruno Wolff III]

On Sun, Mar 04, 2007 at 01:31:26 -0800,
  Justin Zygmont  wrote:
> hi, what I did about this, was to install grub on the second HD:
>
> root (hd1,x)
> find /boot/grub/stage1
> setup (hd1)

If you pull hd0 or it fails in a way where it isn't seen any more, just doing
the above won't work. After doing the above to set things up on hd1, you
should set the root back to hd0 and then do another setup(hd1). That way
when this drive becomes hd0 after a failure, it will be able to find the
files it needs.

[Michael Wiktowy]

On 3/4/07, Bruno Wolff III  wrote:
> On Sun, Mar 04, 2007 at 01:31:26 -0800,
>   Justin Zygmont  wrote:
> > hi, what I did about this, was to install grub on the second HD:
> >
> > root (hd1,x)
> > find /boot/grub/stage1
> > setup (hd1)
>
> If you pull hd0 or it fails in a way where it isn't seen any more, just doing
> the above won't work. After doing the above to set things up on hd1, you
> should set the root back to hd0 and then do another setup(hd1). That way
> when this drive becomes hd0 after a failure, it will be able to find the
> files it needs.

I am just looking into this and from what I understand you have to
install grub on the second disk in a way where it thinks it is the
first disk. you do this with the device command:

device (hd0) /dev/sdb #make grub think hd0 is sdb rather than sda
root (hd0,x) # where x is the your systems root partition on hd0
(which is sdb now)
setup (hd0) # setup grub in hd0 (which is sdb now)

What I can't seem to do is get my RAID1 set to boot in the first
place. I tried to install F7test3 using the SiI 3112 controller (and
consequently dmraid) but it doesn't boot.
So I deleted the RAID set in the RAID BIOS and treated them as
separate drives and the installer says that my platform is unsupported
when I click the Software RAID button in the partitioning step. Has
anyone had success with this setup with previous Fedora releases?
Could I have an old buggy BIOS firmware?

/Mike