Friday, September 02, 2005

Accessing metadevices when booting from CDROM

This does assume that the system isn't using DiskSuite or Veritas,
however - if the system is mirrored, that'll have to be undone[1]
before rebooting after editing anything, otherwise I recall there's the
risk of filesystem corruption.

[1]=For DiskSuite, an overview is at : e/bootcdrom.html. Or, as it's Solaris 9,
he could just load the DiskSuite driver :
http://sunportal.sunmanagers.o rg/pipermail/summaries/2005-Ju ly/006661...

SUMMARY: Accessing metadevices when booting from CDROM?
Guy D. dy7t at
Sun Jul 24 16:28:12 EDT 2005

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Thanks to everyone who responded:

"Santhakumar, Siva" <Siva.Santhakumar at>
"Sandwich Maker" <adh at>
"Thomas M. Payerle" <payerle at>
"Petri Kallberg" <Petri.Kallberg at Sun.COM>

The definitive answer came from Petri who (probably
because of where he works) pointed me to a Sun
document that gives step-by-step directions on
performing this procedure.

It is Document ID: 75210 (Solaris[TM] Volume Manager
Software and Solstice DiskSuite[TM] Software: Mounting
Metadevices) I am not sure if you need to have a Sun
support contract to read it (try searching at for the document ID.) I will just
copy it here for anyone who is interested:

Problem Statement: Top

How can you access data which is located on a
mirrored, RAID5, or a concatenated metadevice when the
system is booted from a CD-ROM into a single user
(For example, reset the root password on a mirrored
root partition.)

Resolution: Top

1) Boot to single user mode using Solaris[TM] 9 OE 1/2

ok boot cdrom -s

2) Find the Solaris[TM] Volume Manager md driver and
unload it.

# modinfo | grep md
38 11d1703 ff9 - 1 md5 (MD5 Message Digest
113 12f1b02 1ecf 70 1 ramdisk (ramdisk driver
127 705c2000 2375a 85 1 md (Solaris Volume
Manager base mod)
# modunload -i 127

For Solaris 9 Operating System (Solaris OS)

3) Mount one of the sub-mirrors of your root
metadevice as read-only to get a copy of metadb
configuration information. NOTE: You'll need to mount
a regular disk device for this step.

# mount -r /dev/dsk/c0t0d0s0 /a
# cp /a/kernel/drv/md.conf /kernel/drv/md.conf
# umount /a

For pre-Solaris 9 OS metadevices:

3) Before Solaris 9 OS, information about metadb's was
stored in the /etc/system file instead of in
/kernel/drv/md.conf and the format used was slightly

Mount one of the sub-mirrors of your root
metadevice as read-only to get a copy of metadb
configuration information. NOTE: You'll need to mount
a regular disk device for this step.

# mount -r /dev/dsk/c0t0d0s0 /a
# cp /a/etc/system /tmp/system
# umount /a

Find metadb information from /tmp/system, for

* Begin MDD database info (do not edit)
set md:mddb_bootlist1="sd:7:16 sd:7:1050
sd:7:2084 sd:15:16
set md:mddb_bootlist2="sd:15:2084"
* End MDD database info (do not edit)

This information can be converted into a format
that Solaris 9 OS understands simply by adding ":id0"
after each metadb identifier. These lines are then
added to the end of /kernel/drv/md.conf.

The previous example would then look like the

mddb_bootlist1="sd:7:16:id0 sd:7:1050:id0
sd:7:2084:id0 sd:15:16:id0

NOTE: Remember to add ";" at the end of each line

4) Load the Solaris Volume Manager md driver and
synchronize meta devices

# modload /kernel/drv/md
# metasync -r

5) READY !! Now you're able to use your existing
metadevices as usual. To view your metadevice
configuration and status, use the metastat command.

# metastat


OK, I did not actually try this, but it looks like it
should work. It still seems like way too much work
to me that I need to add a bunch of lines in cryptic
format to /kernel/drv/md.conf just so it can figure
out where the metadevice database replicates are

Let me add one last story to this drama. Earlier, I
booted the system using a Solaris 9 install CD. But,
I forgot to boot the system with "boot cdrom -s" and
just used "boot cdrom" So, the system booted off the
CD and started running the processes for installing a
new OS (asking me what language I want to use, etc.)
I was using a graphics terminal, so I just ignored
that and opened another xterm window. I was
astonished to see (after a unknown amount of time)
that when I entered "metadb" and "metastat" that I was
able to see all of my existing metadevice databases
and metadevices! But, after another period of time, I
was not! I figured that the Solaris installer must be
smart enough to probe for old metadevices and would
probably offer me the option to retain them if I
continuted to install the OS.

One person assumed that I had a RAID-1 root
filesystem, and suggested that I boot from CD, mount
/dev/dsk/cXdXtXsX (directly specifying a known, good
root partition slice), then change the /etc/vfstab
file on that slice to indicate the root filesystem
should be mounted from /dev/dsk/cXdXtXsX rather than
/dev/md/dsk/dXX, then reboot into that slice.)

Two people pointed out that the default metadb size
became larger starting in Solaris 9 and were worried
that might be causing the trouble. But, this turned
out not to be a factor.

Thanks again for everyone's help

My original question is below:

--- "Guy D." <dy7t at> wrote:

> Hello,
> I have a Solaris 8 system with several RAID 0 and
> 1 filesystems created with Solstice Disk Suite (SDS)
> Now, I believe that SDS was incorporated into
> Solaris
> 9 & 10 (and renamed to Solaris Volume Manager.) I
> was
> wondering how I could access my RAID filesystems if
> I
> lost the root filesystem and had to boot from CD.
> The Solaris 8 CD does not support SDS (it was an
> optional package.) But, I thought if I used a
> Solaris
> 9 or Solaris 10 install CD, I would be able to
> configure them to be able to access the SDS
> metadevices.
> But, when I finally tried it, I was not successful.
> It seemed to me that I should have just needed to
> use
> "metadb -a <slices containing metadb replicates>"
> Any advice for what I need to do? I know where all
> the metadb replicates are located.
> I would think this would be a fairly common task
> (recoving data from metadevices if the root
> filsystem
> failes) but I have not been able to find any
> answers.
> Thanks,
> Doug


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