Does enabling JBOD mode on LSI based controllers affect existing logical disks/arrays?

Question

I've got an LSI2208 integrated raid controller on a Supermicro X9DRH server board. It currently has a Logical Drive (LD) composed of 4 spinning disks. Now I want to add some more drives in JBOD, to let the OS access them directly (as opposed to creating a dedicated RAID0 LD per disk).

There are a couple of links (here for instance) explaining how to enable JBOD mode on LSI2208 controllers. This seems to be an all-or-nothing switch: either JBOD is supported on the controller, or not.

The command:

megacli -AdpSetProp EnableJBOD 1 -a0

... would enable JBOD mode on controller 0

From reading here, it seems that disks plugged into the controller but not associated with a Logical Disk become visible to the OS.

The question: is this a destructive operation? What happens to existing (RAID5/1/0) Logical Disk once this is done ? Or does this only affect disks not yet allocated to a Logical Disk ?

I could just try it out, but that means backing up several TB of data first.

Hope someone has an answer!

Solution

I just tried this on a machine equipped with an LSI 3108. I put in eight drives, set six of them as a RAID6, labeled it, installed a filesystem (XFS), and mounted it. Then I put some data on the mounted FS.

After that, I enabled JBOD mode with storcli64 /c0 set jbod=on the remainig two drives immediately showed up as unix devices, and the existing RAID volume remained untouched. I even verified that by reading and writing to it.

At least on a 3108, I can mix modes. I would be surprised if LSI/Avago would allow a mode switch w/o warning you of a potential problem. Their utilities are pretty solid.

Comments

[Phil Regnauld]

Thanks - this is super helpful. While reviewing the documentation and looking at available commands, I'd accidentally enabled JBOD on a server where I already had RAID volumes configured, and things continued working fine. I quickly reverted when I realized my mistake - so I didn't get to verify JBOD disks showing up. Now I feel a bit safer attempting this :) To @ewwhite: sorry, hadn't seen your comment before now, but it seems it's not destructive...