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Re: Software mirrored hard disk useable on crash

 
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AMI_5
Advisor

Software mirrored hard disk useable on crash

Hi @all,

our hp-ux 11.11 box has 2 hard disks whereby one is used as a mirror. All folders are software mirrored on the second disk (no hardware mirror!!).
Now my question is, if the main disk crashes, can the second disk be used as a replacement of the main disk?

Best Regards

AMI
9 REPLIES 9
Raj D.
Honored Contributor

Re: Software mirrored hard disk useable on crash

Hi AMI,

The answer is yes and obviously mirroring is used for this purpose. If one of the mirroed disk fails the data will be still available on the system , and you need to replace the disk asap, as it will not be able to tolerate any further failure, if the mirror set is set to 1. max can be set to 2.

If it is a root disk , and if the mirroring has been done properly with low quoram and alternate boot path has been set the system will comeup without any intervention.

hth,
Raj.
" If u think u can , If u think u cannot , - You are always Right . "
Raj D.
Honored Contributor
Solution

Re: Software mirrored hard disk useable on crash

AMI,

chek this doc (RootMirror.pdf) for root disk mirroring :

Cheers,
Raj.
" If u think u can , If u think u cannot , - You are always Right . "
AMI_5
Advisor

Re: Software mirrored hard disk useable on crash

Hello Raj D,
Unfortunately I have not installed and configured the system myself to know if everything is done correctly. As I can see, MirrorDisk/UX (B2491BA) software is used. Is there a way to test the second disk without breaking anything or unplugging a disk?

Best Regards,

AMI
Raj D.
Honored Contributor

Re: Software mirrored hard disk useable on crash

Yes ,

You can use this commands to see the mirror status of the root disk:



1.# lvdisplay -v /dev/vg00/lvol3 | grep -i mirror

( If shows "Mirror copies 0 " that means the root disk is not mirrored. For a mirrored disk it should show "Mirror copies 1 or 2 )


2. Also you can check with # lvdisplay -v /dev/vg00/lvol3

(If its mirrored it will show corresponding PE's with two disk.


3. Also # lvlnboot -v


Cheers,
Raj.
" If u think u can , If u think u cannot , - You are always Right . "
Raj D.
Honored Contributor

Re: Software mirrored hard disk useable on crash

Also check this out, this might be useful,


http://www.1402.com/documents/Logical%20Volume%20Manager.pdf

Enjoy,
Cheers,
Raj.
" If u think u can , If u think u cannot , - You are always Right . "
AMI_5
Advisor

Re: Software mirrored hard disk useable on crash

I'm sure all lv's + swap are mirrored but I get following error when running lvlnboot -v :


PROD# lvlnboot -v
Boot Definitions for Volume Group /dev/vg00:
Physical Volumes belonging in Root Volume Group:
/dev/dsk/c8t6d0 (0/0/0/3/0.6.0) -- Boot Disk
/dev/dsk/c0t6d0 (1/0/0/3/0.6.0) -- Boot Disk
Boot: lvol1 on: /dev/dsk/c8t6d0
/dev/dsk/c0t6d0
Root: lvol3 on: /dev/dsk/c8t6d0
/dev/dsk/c0t6d0
Swap: lvol2 on: /dev/dsk/c8t6d0
/dev/dsk/c0t6d0
Dump: lvol2 on: /dev/dsk/c8t6d0, 0

lvlnboot: Volume group not activated.
Cannot display volume group "/dev/vg01".
lvlnboot: Volume group not activated.
Cannot display volume group "/dev/vg02".

This is bad?

I've also found another good link about mirroring hp boxes. It's a bit old but contains some helpful stuff (if someone else has also interest):
http://unix.derkeiler.com/Mailing-Lists/HP-UX-Admin/2003-08/att-0028/root_mirror000.txt

Bill Hassell
Honored Contributor

Re: Software mirrored hard disk useable on crash

> PROD# lvlnboot -v

This shows that the basic LVM structures are correct, that there are two disks (c0t6d0 and c8t6d0) declared as boot devices. However, it does not verify the boot string or boot path in the processor ROMs.

Use these commands to check the boot string:

lifcp /dev/dsk/c0t6d0:AUTO -
lifcp /dev/dsk/c8t6d0:AUTO -

Use this command to check the processor ROMs:

setboot

To make things easier, I've combined several boot query commands into a script: bootinfo which is attached.

> lvlnboot: Volume group not activated.
> Cannot display volume group "/dev/vg01".
> lvlnboot: Volume group not activated.
> Cannot display volume group "/dev/vg02".
> This is bad?

These are secondary volume groups and not required for the system to boot. At some time in the past, an administrator added additional disks and used LVM commands to create vg01 and vg02. They are not activated, probably because they were removed improperly. Look at /var/adm/syslog/syslog.log and /etc/rc.log for error messages.

> I've also found another good link about mirroring hp boxes. It's a bit old ...

It's not old, it's prehistoric (1996-97). ALWAYS use the manufacturer's documentation, especially for your relatively new system. Internet postings can be helpful but always check the accuracy by age and similar docs. Here's the correct documentation for disks and mirroring:

http://docs.hp.com/en/B2355-90950/

specifically:

http://docs.hp.com/en/B2355-90950/ch06s01.html


Bill Hassell, sysadmin
Bill Hassell
Honored Contributor

Re: Software mirrored hard disk useable on crash

And to answer a previous question:

> Is there a way to test the second disk without breaking anything or unplugging a disk?

The command listed above will query the second disk state and a very small portion of the boot content. But if this is a production machine and no one knows if it has ever been tested to see if it will boot from the second disk, it's like hoping that the locks on the doors will work without locking them and that the keys will work without trying them...

You can reboot the system, interrupt the boot process when it says to do so, and then specify the second disk as the boot path.


Bill Hassell, sysadmin
AMI_5
Advisor

Re: Software mirrored hard disk useable on crash

Thanks a lot!!!!