Mirrored UX on HPUX 10.20

[Joe Astrologo]

Hi,

I have a k460 running hpux 10.20. I have 4 disks on controller 0. They consist of 2 root disks and their mirrors.

What is HP's recommendataion on mirrored root disks? Should they be on the same controller or not?


Also, If I want to break an existing mirror and use another disk as the mirror, does that disk have to be non-allocated or can a portion of it be allocated to another logical volume and still be used as a mirror for another volume?

Thanks in advance.

[Patrick Wallek]

I don't know that HP has stated recommendations or not, but I would NOT have my mirrored disks on the same controller. By having everything on the same controller, you are protecting yourself if one of the disks goes bad, but if the controller itself goes bad, then you have serious problems. If you have the mirrors on separate controllers and one controller goes bad, then you can keep the system up until you can schedule down time to replace the bad controller.

If you want to use another disk as a mirror copy, I would make sure that it doesn't contain any information from a differ Volume Group. If it contains information from a different LVOL on VG00, then you could use it. You can use any disk within a VG to mirror to.

I have even seen a situation where both mirror copies were on the same disk. I wouldn't recommend that though.

[Sandor Horvath_2]

Hi !

If You have more then 1 controller I suppose mirror disk to different controller. Otherwise if You have only 1 controller mirror disk on this.
If You use different controller it means your system is protected disk and controller error too.

regards, Saa

[Bill Hassell]

The reason to mirror is for reliability so it doesn't make too much sense to put the mirror on the same channel. If a disk goes bad, it can sometimes lockup the entire channel and nothing can be accessed.

LVM will segregate disks into independent volume groups so you can't allocate space from other volumes. You can mirror to other disks in the same volume group. Typically, you want to put mirror disks onn another channel.

And there is a side benefit to mirroring on different channels: when the read rate on one disk (the read queue) is high, LVM will assign some of the reads to the mirror and now throughput can be twice as fast. Writes will take place in parallel on the mirrors.