Booting from RAID1

Booting from RAID1

[Leslie Rhorer]

Hey, everyone,

	It's me again.  Well, while I am still going to keep small offline
drive backups for my boot drives on the servers, I have decided to replace
the very small boot drives with some slightly larger RAID1 arrays.  To that
end, I've looked around the web for some good advice, and the best I have
found matching my system configuration seems to be this howto:

http://www.linuxhowtos.org/System/raid.htm

	I am a little unsure of one section, however.  In the section he
labels "Fix up initrd" he is suggesting I change the initrd in order to
allow booting from an md array rather than a sata drive.  I thought all 2.6
kernels supported booting from an array directly ( No? ).  Also, both of
these systems will have one PATA drive and one SATA ( seen as a "SCSI"
/dev/sdx drive ) drive in the RAID 1 arrays.  Does that make a difference?

	I will have three RAID 1 arrays: MD1 containing /boot on the first
partition, MD2 containing / on the second partition, and MD3 containing the
swap on the third partition of both drives.  One of the systems will also
have an NTFS partition on each drive for booting Windows - rarely used.  I
will be using grub as the bootloader.

	Any further advice?

Re: Booting from RAID1

[Michael Evans]

On Sat, Dec 19, 2009 at 9:34 PM, Leslie Rhorer <lrhorer@satx.rr.com> wrote:
>
> Hey, everyone,
>
>        It's me again.  Well, while I am still going to keep small offline
> drive backups for my boot drives on the servers, I have decided to replace
> the very small boot drives with some slightly larger RAID1 arrays.  To that
> end, I've looked around the web for some good advice, and the best I have
> found matching my system configuration seems to be this howto:
>
> http://www.linuxhowtos.org/System/raid.htm
>
>        I am a little unsure of one section, however.  In the section he
> labels "Fix up initrd" he is suggesting I change the initrd in order to
> allow booting from an md array rather than a sata drive.  I thought all 2.6
> kernels supported booting from an array directly ( No? ).  Also, both of
> these systems will have one PATA drive and one SATA ( seen as a "SCSI"
> /dev/sdx drive ) drive in the RAID 1 arrays.  Does that make a difference?
>
>        I will have three RAID 1 arrays: MD1 containing /boot on the first
> partition, MD2 containing / on the second partition, and MD3 containing the
> swap on the third partition of both drives.  One of the systems will also
> have an NTFS partition on each drive for booting Windows - rarely used.  I
> will be using grub as the bootloader.
>
>        Any further advice?
>
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>

Advice point 1; read my howto: http://wiki.tldp.org/LVM-on-RAID  If
you see anything that doesn't work, let me know so I can fix it.

Advice point 2; which my howto should mention: For boot devices you'll
probably want to use the 1.0 mdadm label format (not 1.1 or 1.2, which
are the same but change where the label is stored) for just the boot
raid 1.0 only.  It will also mention some things you should be extra
careful about...

Like mounting the bare devices in that raid set by mistake.

Oh, and you'll also very likely want grub to read the /boot
filesystem, which is why it must be on a partition followed by the
raid header, instead of a partition containing a raid header and raid
protected partition.  That use is OK since grub operates read-only.
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RE: Booting from RAID1

[Leslie Rhorer]

> Advice point 1; read my howto: http://wiki.tldp.org/LVM-on-RAID  If
> you see anything that doesn't work, let me know so I can fix it.

	I read through it, thanks.  I'll let you know if anything you
mention is broken -although I doubt it.

> Advice point 2; which my howto should mention: For boot devices you'll
> probably want to use the 1.0 mdadm label format (not 1.1 or 1.2, which
> are the same but change where the label is stored) for just the boot
> raid 1.0 only.

Oops!  I already created a 1.2 Superblock.  Well, no biggie.  I'll just
trash it and do it over.  The /boot array is tiny, so it doesn't take long
at all to create.

>  It will also mention some things you should be extra
> careful about...
> 
> Like mounting the bare devices in that raid set by mistake.

	Uh... yeah.  That could be ugly.  That's why I like to have a cold
drive on the shelf configured with the entire OS.

> Oh, and you'll also very likely want grub to read the /boot
> filesystem, which is why it must be on a partition followed by the
> raid header, instead of a partition containing a raid header and raid
> protected partition.  That use is OK since grub operates read-only.

	I think I follow you, here.  IOW, partition the drive, create the md
target, and then format the RAID array, right?  Or are you saying one should
format the partition and then create the RAID array on top of it?

RE: Booting from RAID1

[Leslie Rhorer]

> >> Oh, and you'll also very likely want grub to read the /boot
> >> filesystem, which is why it must be on a partition followed by the
> >> raid header, instead of a partition containing a raid header and raid
> >> protected partition.  That use is OK since grub operates read-only.
> >
> >        I think I follow you, here.  IOW, partition the drive, create the
> md
> > target, and then format the RAID array, right?  Or are you saying one
> should
> > format the partition and then create the RAID array on top of it?
> >
> >
> 
> It works much more cleanly if you create the RAID array first, and
> then use the container it provides; 

	Now I definitely don't follow you.  Are you saying one should create
an array from the raw drive, partition it, format the first partition, then
create secondary arrays from the second and third partition, and finally
format the second and third array?

> this way the end of your file-system does not overlap the raid super-
> block.

	I can follow that - there's a danger of wiping or moving the mdadm
superblock if it is contained in the filesystem, but it seems to me
partitioning the drive and then creating the array from a partition, as I
first suggested, will accomplish that just fine.

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Re: Booting from RAID1

[Michael Evans]

On Sun, Dec 20, 2009 at 7:37 AM, Leslie Rhorer <lrhorer@satx.rr.com> wrote:
>> >> Oh, and you'll also very likely want grub to read the /boot
>> >> filesystem, which is why it must be on a partition followed by the
>> >> raid header, instead of a partition containing a raid header and raid
>> >> protected partition.  That use is OK since grub operates read-only.
>> >
>> >        I think I follow you, here.  IOW, partition the drive, create the
>> md
>> > target, and then format the RAID array, right?  Or are you saying one
>> should
>> > format the partition and then create the RAID array on top of it?
>> >
>> >
>>
>> It works much more cleanly if you create the RAID array first, and
>> then use the container it provides;
>
>        Now I definitely don't follow you.  Are you saying one should create
> an array from the raw drive, partition it, format the first partition, then
> create secondary arrays from the second and third partition, and finally
> format the second and third array?
>
>> this way the end of your file-system does not overlap the raid super-
>> block.
>
>        I can follow that - there's a danger of wiping or moving the mdadm
> superblock if it is contained in the filesystem, but it seems to me
> partitioning the drive and then creating the array from a partition, as I
> first suggested, will accomplish that just fine.
>
>

It is an option to partition it after the fact; however generally it's
better to partition it first, and then apply whatever raid level you
like to each partition.

You misunderstand on the second half; the danger is that both the
'filesystem' and 'mdadm superblock' attempt to use the whole device.
That may appear to work for a while, but there is danger that the
filesystem could grow and store data in the same place the mdadm
superblock is; depending on if the filesystem or mdadm then filesystem
within the device was used this will either fail, or destroy the raid
information block.
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Re: Booting from RAID1

[Goswin von Brederlow]

Michael Evans <mjevans1983@gmail.com> writes:

> Advice point 2; which my howto should mention: For boot devices you'll
> probably want to use the 1.0 mdadm label format (not 1.1 or 1.2, which
> are the same but change where the label is stored) for just the boot
> raid 1.0 only.  It will also mention some things you should be extra
> careful about...
>
> Like mounting the bare devices in that raid set by mistake.
>
> Oh, and you'll also very likely want grub to read the /boot
> filesystem, which is why it must be on a partition followed by the
> raid header, instead of a partition containing a raid header and raid
> protected partition.  That use is OK since grub operates read-only.

How far is the support for all superblock formats in grub2?

MfG
        Goswin

RE: Booting from RAID1

[Leslie Rhorer]

	Well, after a bent pin on a tray connector prevented drive in the
tray being recognized, and then a memory stick poppingt out of its socket
unbeknownst to me, I tried rebooting the system, but the primary drive had
its file systems locked, and none of the boot CDs I have on hand have
reiserfs on them.  The secondary drive also would no longer boot.  I loaded
a brand new Debina install on a spare disk, but when I tried to load mdadm
or reiserfsprogs (or anything else), the system could not reach the outside
world.  I could download files from any server on my LAN, but anything on
the internet was no-go.  So I installed Debian again from scratch, and
finally I have a working system, again.  Phew!!  (Sorry, I just had to
vent.)

	Anyway, now that my original drive is back in good shape, I want to
get the secondary RAID drive working so I can then copy everything to a
primary RAID drive and have a fully functional RAID boot system.  The
problem is, when I boot from the disc, during the boot mdadm complains: "No
devices listed in conf file were found", and then the system hangs.
Clearly, the boot loader is finding the kernel in md1 / sdx1, but it seems
the md2 / sdx2 array is not being properly loaded by the kernel.  Here are
the contents of /etc/mdadm/mdadm.conf:

# mdadm.conf
#
# Please refer to mdadm.conf(5) for information about this file.
#

# by default, scan all partitions (/proc/partitions) for MD superblocks.
# alternatively, specify devices to scan, using wildcards if desired.
DEVICE partitions
DEVICE /dev/hda* /dev/sd[a-i]*

# auto-create devices with Debian standard permissions
CREATE owner=root group=disk mode=0660 auto=yes

# automatically tag new arrays as belonging to the local system
HOMEHOST <system>

# instruct the monitoring daemon where to send mail alerts
MAILADDR lrhorer@satx.rr.com

# definitions of existing MD arrays

# This file was auto-generated on Thu, 14 May 2009 20:25:57 -0500
# by mkconf $Id$
PROGRAM /usr/bin/mdadm_notify
ARRAY /dev/md0 level=raid5 metadata=1.2 num-devices=7
UUID=940ae4e4:04057ffc:5e92d2fb:63e3efb7 name='Backup':0
ARRAY /dev/md3 level=raid1 num-devices=2 metadata=01.02 name='Backup':3
UUID=3615c4a2:33786b6d:b13863d9:458cd054
ARRAY /dev/md2 level=raid1 num-devices=2 metadata=01.02 name='Backup':2
UUID=d45ff663:9e53774c:6fcf9968:21692025
ARRAY /dev/md1 level=raid1 num-devices=2 metadata=01.00 name='Backup':1
UUID=d6a2c60b:7345e957:05aefe0b:f8d1527f

	And here are the contents of the /boot/grub/menu.lst file:

# menu.lst - See: grub(8), info grub, update-grub(8)
#            grub-install(8), grub-floppy(8),
#            grub-md5-crypt, /usr/share/doc/grub
#            and /usr/share/doc/grub-legacy-doc/.

## default num
# Set the default entry to the entry number NUM. Numbering starts from 0,
and
# the entry number 0 is the default if the command is not used.
#
# You can specify 'saved' instead of a number. In this case, the default
entry
# is the entry saved with the command 'savedefault'.
# WARNING: If you are using dmraid do not change this entry to 'saved' or
your
# array will desync and will not let you boot your system.
default         0

## timeout sec
# Set a timeout, in SEC seconds, before automatically booting the default
entry
# (normally the first entry defined).
timeout         5

# Pretty colours
color cyan/blue white/blue

## password ['--md5'] passwd
# If used in the first section of a menu file, disable all interactive
editing
# control (menu entry editor and command-line)  and entries protected by the
# command 'lock'
# e.g. password topsecret
#      password --md5 $1$gLhU0/$aW78kHK1QfV3P2b2znUoe/
# password topsecret

#
# examples
#
# title         Windows 95/98/NT/2000
# root          (hd0,0)
# makeactive
# chainloader   +1
#
# title         Linux
# root          (hd0,1)
# kernel        /vmlinuz root=/dev/hda2 ro
#

#
# Put static boot stanzas before and/or after AUTOMAGIC KERNEL LIST

### BEGIN AUTOMAGIC KERNELS LIST
## lines between the AUTOMAGIC KERNELS LIST markers will be modified
## by the debian update-grub script except for the default options below

## DO NOT UNCOMMENT THEM, Just edit them to your needs

## ## Start Default Options ##
## default kernel options
## default kernel options for automagic boot options
## If you want special options for specific kernels use kopt_x_y_z
## where x.y.z is kernel version. Minor versions can be omitted.
## e.g. kopt=root=/dev/hda1 ro
##      kopt_2_6_8=root=/dev/hdc1 ro
##      kopt_2_6_8_2_686=root=/dev/hdc2 ro
# kopt=root=/dev/hda2 ro

## default grub root device
## e.g. groot=(hd0,0)
# groot=(hd0,0)

## should update-grub create alternative automagic boot options
## e.g. alternative=true
##      alternative=false
# alternative=true

## should update-grub lock alternative automagic boot options
## e.g. lockalternative=true
##      lockalternative=false
# lockalternative=false

## additional options to use with the default boot option, but not with the
## alternatives
## e.g. defoptions=vga=791 resume=/dev/hda5
# defoptions=quiet

## should update-grub lock old automagic boot options
## e.g. lockold=false
##      lockold=true
# lockold=false

## Xen hypervisor options to use with the default Xen boot option
# xenhopt=

## Xen Linux kernel options to use with the default Xen boot option
# xenkopt=console=tty0

## altoption boot targets option
## multiple altoptions lines are allowed
## e.g. altoptions=(extra menu suffix) extra boot options
##      altoptions=(single-user) single
# altoptions=(single-user mode) single

## controls how many kernels should be put into the menu.lst
## only counts the first occurence of a kernel, not the
## alternative kernel options
## e.g. howmany=all
##      howmany=7
# howmany=all

## should update-grub create memtest86 boot option
## e.g. memtest86=true
##      memtest86=false
# memtest86=true

## should update-grub adjust the value of the default booted system
## can be true or false
# updatedefaultentry=false

## should update-grub add savedefault to the default options
## can be true or false
# savedefault=false

## ## End Default Options ##

title           Debian GNU/Linux, kernel 2.6.26-1-amd64  Disk 1
root            (hd0,0)
kernel          /vmlinuz-2.6.26-1-amd64 root=/dev/md2 ro quiet
initrd          /initrd.img-2.6.26-1-amd64

title           Debian GNU/Linux, kernel 2.6.26-1-amd64  Disk 2
root            (hd11,0)
kernel          /vmlinuz-2.6.26-1-amd64 root=/dev/md2 ro quiet
initrd          /initrd.img-2.6.26-1-amd64


title           Debian GNU/Linux, kernel 2.6.26-1-amd64 (single-user mode)
root            (hd0,0)
kernel          /vmlinuz-2.6.26-1-amd64 root=/dev/hda2 ro single
initrd          /initrd.img-2.6.26-1-amd64

### END DEBIAN AUTOMAGIC KERNELS LIST

RE: Booting from RAID1

[Leslie Rhorer]

Nevermind.  I was able to move the drives around and get the boot working.