Re: Force assemble 6 disk raid5 degraded array from 4 good disks, 1 stale disk, 1 missing/corrupt disk ?

> The sd# order was changed by the 3ware card,  and i don't understand the
> different device numbering schemes.

This I can help with as I ran into the same problem with an 8
port 9550SX.  The 3Ware card presents the block devices in the
order of their unit numbers, not port numbers.  Typically, when
the devices are initially setup, a person starts with port 0 and
creates unit 0.  Port 1 exports as Unit 1 and so on (as logic would
suggest).  When a device fails, say Unit 2 (which in this example
would be on Port 2) you remove the device and insert a new Hard
Drive attached to Port 2.  In a 4 drive setup (all being exported
as single devices) the replacement drive would show up as Unit 4
(the fifth exportable unit).

### Before 

Port 0 -> Unit 0 -> sda
Port 1 -> Unit 1 -> sdb
Port 2 -> Unit 2 -> sdc
Port 3 -> Unit 3 -> sdd

### After

Port 0 -> Unit 0 -> sda
Port 1 -> Unit 1 -> sdb
Port 2 -> Unit 4 -> sdd
Port 3 -> Unit 2 -> sdc


I downloaded 3Ware's CLI utility and tried adjusting the Unit
order, but I could not find a way to do this.  I called their
Tech support and I was told that the only way to re-order the
Unit #'s was thru the setup/BIOS utility (alt-3 at boot time).
Once in the setup utility, you can use the PageUp/PageDown keys
to re-order the Units.

As for the re-assembling the MD device, I'm not sure.  I'm not
much of an EVMS expert here but I know you can re-create the
array with mdadm using the --assume-clean switch.  This has
worked for me in the past, the only difference being that the
array was NOT managed with EVMS.  I'm not even sure if mdadm can
assemble an MD device that EVMS as created/managed without doing
some kind of conversion first.  Someone on the list should be
able to help you out with the EVMS way to re-assemble the array.
Either way, I would make sure your devices are getting discovered
in the correct order before trying to assemble the degraded array. 

~Bryan

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