lvm mirroring

Hello,

I have 2 physical discs.
I have 4 partitions on the first disk.
I created a volume group "lvmhd" from all of the partitions and later created logical volumes.

this is the result from the vgdisplay
--- Volume group ---

VG Name               lvmhd
VG Access             read/write
VG Status             available/resizable
VG #                  0
MAX LV                256
Cur LV                3
Open LV               3
MAX LV Size           2 TB
Max PV                256
Cur PV                4
Act PV                4
VG Size               35.59 GB
PE Size               32 MB
Total PE              1139
Alloc PE / Size       1131 / 35.34 GB
Free  PE / Size       8 / 256 MB
VG UUID               xqamqE-9gSs-Xy3O-2tVQ-wYzy-Cp3u-0Wivbd

and those are the logical volumes

/dev/lvmhd/lvm_usr    3.0G  980M  1.8G  35% /usr
/dev/lvmhd/lvm_var    4.9G   65M  4.6G   2% /var

/dev/lvmhd/lvm_home 27G 33M 25G 1% /home

later I mirrored the first disk to the second disk with dd if=/dev/hda of=/dev/hdb so if the first disk breaks I can remove it and replace it with the second disk and get the server up in minutes.

Now I want to be able to use the second disk while I am running from the first. But the volume groups are the same and I am afraid that if I will recreate the logical volumes I'll ruin some thing on the second disk. Is there anything I can do about it so I could use the second disk for backups but still have the same architecture as the primary disk ?
is there any way to mount those logical volumes which are mirrors of the primary disk ?
for example I can do
pvdisplay /dev/hdb3 (this is the slave disk which is the mirror of the primary and its not mounted)
--- Physical volume ---

PV Name               /dev/hdb3
VG Name               lvmhd
PV Size               13.67 GB [28676025 secs] / NOT usable 32.19 MB [LVM: 129 KB]
PV#                   1
PV Status             available
Allocatable           yes (but full)
Cur LV                3
PE Size (KByte)       32768
Total PE              436
Free PE               0
Allocated PE          436
PV UUID               5XenPH-2NLb-cmN0-qEBb-QGuJ-zWxv-otMr7i

thanks

This is a copy, no mirror.

With LVM1 rename /dev/hdb to /dev/myhdb, with LVM2 you could change the device name filter in a configfile.

You would need to change the LVM metadata to do this.

The correct way to have a copy of your VG would have been
to create a second VG which must have a different name from the first one with PV hdb in it, create all the LVs you have in "lvmhd", which can have the same names as in "lvmhd" and dd the LVs over.

I presume your VG "lvmhd" takes no writes during the copy.

Regards,
Heinz    -- The LVM Guy --

*** Software bugs are stupid.
    Nevertheless it needs not so stupid people to solve them ***

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Heinz Mauelshagen                                 Sistina Software Inc.
Senior Consultant/Developer                       Am Sonnenhang 11
                                                  56242 Marienrachdorf
                                                  Germany
[email protected]                           +49 2626 141200
                                                       FAX 924446
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