lvm guru's

[Donny Jekels]

we have a large volume that is striped at 32k over 4 disks. I am not sure if pvremove will do the trick. or lvreduce.

but can anyone please let me know how I can safely remove one of the disk from the volume without taking the thing offline? we have adv jfs.

[Pete Randall · Accepted solution]

Donny,

I can't even begin to imagine how you could remove one of the disks without destroying the striped lvol. I honestly don't think there is a way without recreating the whole thing.


Pete

[Stefan Farrelly]

If its mirrored then you can remove one of the drives without taking the volume online, if its NOT mirrored then NO you cant.

If you have a spare disk of the same PE size as the one you want to remove then you CAN use pvmove to move the old disk to the new one, then you can vgreduce the old disk and physically pull it. We use pvmove all the time, its nice and safe.

[Donny Jekels]

one of the many reasons why I hate lvm stiping.

thanx, just wanted to make 100% sure.

[Donny Jekels]

stephen,

please explain how you can mirror a striped volume with lvm?

[Pete Randall]

Donny,

I hate to speak for Stefan, but I believe he's referring to mirroring using the MirrorDisk/UX product. LVM provides no mirroring capabilities on its own.


Pete

[A. Clay Stephenson]

Look at the man pages for lvcreate: specifically at the section that refers to EXTENT-BASED MIRRORED STRIPES. It will explain how to set these up. There is very little performance benefit to be gained from these because the smallest possible PE (1MB) is far too large to be a good stripe size.

[Stefan Farrelly]

Pete,

True, you need Mirrorux to pull one on the fly, but you dont need it, you can use pvmove anytime as long as you have a spare disk of the same PE size to add to your VG.

[Donny Jekels]

we have mirrordisk/ux. except extent base mirror'ing - I don't think you can mirror a striped volume even with mirrordisk/ux.

that will be a raid 0+1 which is not supported by lvm.

[Pete Randall]

Stefan,

Thanks, I'm still trying to digest that concept.

To my way of thinking, if you've got a file system striped over 4 physical disks and you pull one of them out, your file system is going to have issues, isn't it? Granted you can pvmove the fourth disk, but this would have to be done before pulling said fourth disk, wouldn't it?


Pete