Triple Mirroring

[David_492]

Dear All

Can i do triple mirroring over hp unix server rp8400 which has 4 disks?

Thank you

[Stefan Farrelly]

You can only have a max of 2 mirror copies in LVM. ie. 1 disk, mirrored twice (to disks 2 and 3). So with 4 disks you can use one for data, mirrored once to disk2 and once to disk3 leaving disk4 free.

[Pete Randall]

David,

Assuming you have the MirrorDisk/UX product, yes, you can.


Pete

[Hoefnix]

If you mean that you like to have 2 mirror copies of the data to separate disks. Yes that is possible.
If you have MirrorDisk/UX installed.

You should create all physical volumes using pvcreate and extend the volumegroup that you want to mirror.

After that you can extend the logicalvolumes using lvextend:
lvextend -m 2 lv_path

[Steve Lewis]

Yes, but in my opinion, there is little point in doing so. You get better performance using more disks with just one mirror copy. This is because LVM always tries to read from the first disk in the VG first, only to second in the first is busy and so on.

I tried a 3-way mirror once, but the write performance was awful.

If you are really adamant about a 3 way mirror then you might like to try this sort of scheme to spread the load evenly on writes.
lvolA on disk 1, mirror to disk 2 and 3
lvolB on disk 2, mirror to disk 3 and 4
lvolC on disk 3, mirror to disk 4 and 1
lvolD on disk 4, mirror to disk 1 and 2

points please