Re: can you help explain some --examine output to me?

["Keld Jørn Simonsen" <keld@dkuug.dk>]

On Sat, Dec 20, 2008 at 12:16:01PM +1100, NeilBrown wrote:
> On Sat, December 20, 2008 11:34 am, Jon Nelson wrote:
> > As part of the output from --explain (on a raid1 with a 1.0 metadata),
> > I see this:
> >
> >     Array Slot : 3 (failed, failed, 0, 1)
> >    Array State : uU 2 failed
> >
> > I read the first line as "This device is using slot 3. slot 0 is
> > failed, slot 1 is failed, slot 2 is RaidDevice 0, slot 3 is RaidDevice
> > 1" where RaidDevice is the same as in the output for --detail. Is that
> > correct?
> >
> > The second line is more opaque. What to little-u and big-u mean? Does
> > "2 failed" mean the raid thinks two devices have failed?
> >
> 
> Yes, it is rather cryptic...
> 
> Every device in a 1.x array is assigned a 'slot' number.  This number is
> stable - it never changes.
> 
> Each device in the array also has a 'role' number indicating its current
> role in the array, which is either to be a spare or to have a position
> (0, 1, ...) in the array.
> 
> The output you produces says that this device occupies slot 3.
> It then notes that:
>   the device which occupied slot 0 has failed
>   the device which occupied slot 1 has failed
>   the device which occupies slot 2 has role 0
>   the device which occupies slot 3 has role 1
> 
> Then it shows you the state which indicated how the different
> roles are going.
>    uU
> means that both roles are 'up', and the 'this' device has the second
> role (capital U for 'this' device).
> Two devices have previously failed.
> 
> I should probably get rid of that '2 failed' bit, it isn't helpful.
> I should probably report 'empty' rather than 'failed' in the 'Array Slot'
> line.
> 
> Note that if you fail a devices, remove it, then add it back in such that
> it doesn't appear to be a re-add, it will be treated like a new
> device and get a new slot number.  (after all the old device was faulty,
> this one isn't so it must be a new device ?).
> I should probably get it to re-use the slot number in that case.
> 
> And I should probably document some of this.

Oh, well, you just did :-). I added this to the mdadm FAQ wiki page.

keld