Disk Mirroring different HD sizes

[Fernando Vienrich]

Hi guys I want to make sure I'm organizing will my new server installation:

I have 4 internal 36 Gbytes HDs, and 4 external 18 Gbytes HDs (Rack system).

I have vg00, vg01, vg02, vg03. The primary HDs will be the internal for each vg. The external will be the mirror for each one of the internal.
In reference to the mismatch of sizes between Primary and mirrored, do I just have to assign 18Gbytes to each VG when creating the vg on each 36 gbytes HD?
Does this difference on size will my system response slow??

thanks for any feedback.

Fernando.

[Marco Santerre]

I doubt very much that the difference in size will make a difference on the system response time, but.. but it will only allow you to mirror only 18 out of the possible 36 gigs. Because you can't mirror on the same disk that means you'll have to use the external disk to mirror the internal and therefore, the limitation youhave is due to the size of your external disk (18 gig).

[A. Clay Stephenson]

First of all, mirrors are done at the logical volume level, not at the disk level. Using your scheme, you will need to create the VG's using the 36GB drives and then vgextend with the 18GB drives. Your problem is that you will need to leave 18GB's on each disk as unallocated space if you plan to mirror each LVOL.

Note: If your internal disks are on different controllers then you can mirror internally and not "waste" space and for that matter it is perfectly okay to use the external disks as boot devices.

[John Carr_2]

Hi

mirror disk works on logical volume mirroring and it is actually possible i believe to mirror a logical volume on the same disk, not that it would be of any benefit.

would you not be better off to mirror 2*36 and 2*18 rather than wasting 18GB on each of the 4 36GB disks !

:-)

[Helen French]

I guess you are talking about software mirroring using Mirror/UX. If yes, then the mirroring is done on logical volume level and not in physical hardware.

The mirroring will be between logical volumes resides in internal disk and the same amount of space (LV) in an external disk. You can do this for the 18GB space, but not for the rest 18GB. What I would suggest you to do is mirror your root disk fully and the data one partially if needed.

The unmirrored 18GB can be used for normal data storage.

[Fernando Vienrich]

Thanks Guys for the responses. I have other limitations of my database application too that require to have Vg01 and Vg02 each in different HD location. So I guess is OK to proceed as planned initially regardless of loosing some space in the primary 36 Gb.HDs.

thanks,

Fernando.

[Helen French]

Again, you don't need to waste some space on the 36GB disk. Create LVs with 18GB and mirror it with external disk. The remaining 18GB can be used to create other LVs which need not be mirrored.

[Sunil Sharma_1]

Hi,

you can very well do it without wasting any space becoz in LVM mirroring is working on the basis of volume.

so you can some volumes and rest can be without mirrored.

Sunil