RE: Converting a non-RAID RedHat System to run on Software RAID

RE: Converting a non-RAID RedHat System to run on Software RAID

[Cress, Andrew R]

Here's my current info on how to build a root mirror with software RAID.
   http://scsirastools.sourceforge.net/docs/UserGuide (section 4.0)
I used the HOWTO, with some things added that I learned along the way.
The 15 steps are scripted, and the scripts are broken out in the CVS
tree as files/md*.sh

The instructions are oriented to lilo, but the grub equivalent is
scripted in files/mdevt script:
http://cvs.sourceforge.net/cgi-bin/viewcvs.cgi/*checkout*/scsirastools/s
csirastools/files/mdevt?rev=HEAD&content-type=text/plain

Andy

-----Original Message-----
From: Eric Wood [mailto:eric@interplas.com] 
Sent: Tuesday, September 09, 2003 2:18 PM
To: linux-raid@vger.kernel.org
Subject: Converting a non-RAID RedHat System to run on Software RAID


I frequently want to convert an existing single drive install of RH
linux
into a mirrored RAID-1 set.  So I thought I found the holy grail:

http://unthought.net/Software-RAID.HOWTO/Software-RAID.HOWTO-4.html#ss4.
14

However, it is slightly out dated (RH 7.1 days).  Since I'm trying to
mirror
RH 9, I have several questions based on this HOWTO:

1. Sect. 4.14.6: /dev/md0 already existed while in rescue mode.  Ignored
it,
no problem
2. Sect. 4.14.7: I could not umount /mnt/sysimage to save my life.
Looking
at what was mounted, I seen that I needed to also umount
/mnt/sysimage/dev/pts.  I cd'd into the / directory to make sure I
wasn't
holding the unmount up.  So I could not proceed with the howto.

3. Sect. 4.14.11,12 should be updated to include grub.

4. Sect. 4.14.14.  Do I first have to convert from ext3 back to ext2?
Since
I use ext3 does this step still apply or does mkraid at the second
superblock in an acceptable manor for ext3?  Do I still have to
resize2fs
the md devices?

Any info I gather, I will relay to the howto author and hopefully he'll
come
out with an update.
thanks,
-eric wood

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Re: Converting a non-RAID RedHat System to run on Software RAID

[Bill Rugolsky Jr.]

On Tue, Sep 09, 2003 at 02:37:18PM -0400, Cress, Andrew R wrote:
> The instructions are oriented to lilo, but the grub equivalent is
> scripted in files/mdevt script:
> http://cvs.sourceforge.net/cgi-bin/viewcvs.cgi/*checkout*/scsirastools/s
> csirastools/files/mdevt?rev=HEAD&content-type=text/plain

A word of caution:

One miserable consequence of using GRUB on RAID1 is inadvertent corruption
of (a small part of the) RAID-1 /boot partition.  Since grub (at least
in Red Hat Rawhide) doesn't grok MD, if one sets up a RAID-1 /boot
partitiion, say

   /dev/md1 ->  (/dev/sda1,dev/sdb1),

then modifications made at the grub prompt modify the filesystem and
desynchronizes the RAID1 set. [It seems that simply using 'e' to edit the
kernel args has this effect, though I haven't verified it myself.]  We see
this corruption in MD5 variation in our nightly integrity-verification
cron job.

Grub has a --read-only option when running the grub shell from Linux;
I haven't yet found the time to delve into the code to see whether it
is simple to do the same in the stage2 loader, or whether the read-only
behavior is purely a function of the device open() when running the grub
shell.

Trivial workaround is to resync the second drive in the rc scripts;
for the typical 50-100MB /boot partition, this takes only a few seconds.
 
Regards,

	Bill Rugolsky

Re: Converting a non-RAID RedHat System to run on Software RAID

[Eric Wood]

I may be wrong but simply 'e'diting the boot menu at boot time doesn't write
back anything to the filesystem.  I edit my boot string all the time to try
out all sorts of kernel arguments like "ide=nodma" and upon the next reboot
that modification is gone.  Until you actually put it in
/boot/grub/grub.conf is won't stick or do an "install" from within grub,
then I can't see why grub is altering your /boot filesystem to get the
mirror out of sync.  Sounds like a bug!
-eric wood

Bill Rugolsky Jr. wrote:
> desynchronizes the RAID1 set. [It seems that simply using 'e' to edit
> the kernel args has this effect, though I haven't verified it
> myself.]  We see this corruption in MD5 variation in our nightly
> integrity-verification cron job.
>
> Trivial workaround is to resync the second drive in the rc scripts;
> for the typical 50-100MB /boot partition, this takes only a few
> seconds.
>
> Bill Rugolsky

Converting a non-RAID RedHat System to run on Software RAID

[Eric Wood]

I frequently want to convert an existing single drive install of RH linux
into a mirrored RAID-1 set.  So I thought I found the holy grail:

http://unthought.net/Software-RAID.HOWTO/Software-RAID.HOWTO-4.html#ss4.14

However, it is slightly out dated (RH 7.1 days).  Since I'm trying to mirror
RH 9, I have several questions based on this HOWTO:

1. Sect. 4.14.6: /dev/md0 already existed while in rescue mode.  Ignored it,
no problem
2. Sect. 4.14.7: I could not umount /mnt/sysimage to save my life.  Looking
at what was mounted, I seen that I needed to also umount
/mnt/sysimage/dev/pts.  I cd'd into the / directory to make sure I wasn't
holding the unmount up.  So I could not proceed with the howto.

3. Sect. 4.14.11,12 should be updated to include grub.

4. Sect. 4.14.14.  Do I first have to convert from ext3 back to ext2? Since
I use ext3 does this step still apply or does mkraid at the second
superblock in an acceptable manor for ext3?  Do I still have to resize2fs
the md devices?

Any info I gather, I will relay to the howto author and hopefully he'll come
out with an update.
thanks,
-eric wood