Mirrored drive and physical disk size

[John R Johnson]

I need to replace a drive in a couple mirrored systems. But never really thought about this until now. I have a couple systems that are mirrored using 9G disks. Since 9G disks are items of the far distant past, has anyone mounted various size disks on a mirrored system? The replaced disk would become the mirror alevating potential space issues. I have not tried this myself and supposed it would be worth a shot just to see the results. I would even be willing to make this a two step drive replacement. Once the newly installed disk was sync'd to the original 9G and then replace the 9G disk with an identical size.

Any thoughts?

[RAC_1 · Accepted solution]

While you can use disks greater than that. e.g. if one disk is 9gb disk, you can still mirror it onto 36/72 gb disks. But as you understand, you will not be able to use full of it's size.

Anil

[Robert-Jan Goossens_1]

John,

add on to Anil's answer.

The problem is the "max pe per pv" in your volume group configuration.

# vgdisplay -v vg00
--- Volume groups ---
VG Name /dev/vg00
Max PE per PV 2500
PE Size (Mbytes) 4

Above will limit your new disks to 10 GB.

If you have the time and money, recreate your volume group and resore the data from tape.

Hope this will help,
Robert-Jan

[Devender Khatana]

Hi,

Yes, just check the parameter Max_PE_PerPV and PE_Size from the output of vgdisplay -v /dev/vgxx and you will be able to know wheather you can utilize whole of your disk or not if you mirror it with existing low capacity disks.

You might get escaped of recreating VG and restoring data if care was taken for expandability while VG was created in past.

Another simple way of doing it is to create new VG and logical volumes on new sets of disks and mount it on some different path, Copy data from the current disks to the new disks & then mount new disks on the current path and see if everything is fine. Once you are sure everything is functional with old disks unmounted, You can remove old disks after exporting that VG.

But always take and test backup before doing this.

HTH,
Devender

[John R Johnson]

Thanks for the feedback.

I've got 10.2 running on 5 - 735 machines using HFS (root and data disk -- 2 disk configuration and non-mirrored).
2 systems are running 10.2 - on C360 machines using LVM (mirrored).
9 systems running 10.2 - on C360 machines using VxFS/JVM.

Until a few months ago all but 3 of the systems were 735 machines on a two disk root/data configuration. The addition of the C360 machines & mirroring have saved the sweat & tears! These machines are used in truck loading automation with multiple devices and Oracle. Everything running on the machines have been much happier and the CPU never breaks sweat anymore. There was little to justify the replacement of the other 5 machines with C360's. The old 735 machines over the past 8 years have proven themselves to be a workhorse!

But it has been nice to put several of them "down" so to speak.

Again thanks for all your help.

[John R Johnson]

Thanks again.

JJ