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Phil Regnauld
Asked: 2016-12-03 15:10:06 +0800 CST

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

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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!

lsi jbod megacli

1 Answers

  1. 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.

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