Ubuntu :: MDADM - How To Determine Which Drive Has Failed

I know this is probably a very generic linux question, but since I am using ubuntu - I thought it safer to ask here. I have jumped into the deep end of linux - and I am afraid that I will be forced to swim sooner rather than later.

Let me start at the beginning - I am and probably will be a windows fan for a long time - let me not list the reasons - or else you guys will probably hang met out to dry - the one thing I have discovered - is that windows sucks in generating a software RAID - especially the RAID 5 that i was looking for any case - after loosing plenty data via windose - I decided to attempt linux/ ubuntu. I must say - so far so good.

I used this excellent guide: [URL] and must say that the raid is performing admirably - I am currently busy adding/growing the 12th 1Tb drive onto the RAID, and no issues so far(some other major WOW advantages i have noticed... like speed writing too and reading from the RAID.. )

See below MDstat outputcat proc mdstat:
Personalities : [linear] [multipath] [raid0] [raid1] [raid6] [raid5] [raid4] [raid10]
md0 : active raid5 sdl1[11] sdj1[10] sdb1[1] sdm1[6] sdk1[2] sdi1[8] sdh1[0] sdg1[3] sdf1[4] sde1[9] sdd1[5] sdc1[7]
9767599360 blocks super 0.91 level 5, 64k chunk, algorithm 2 [12/12] [UUUUUUUUUUUU]
[==========>..........] reshape = 50.7% (495864576/976759936) finish=1482.0min speed=5407K/sec
unused devices: <none>

My questions :
If one drive fails on the array(for example SDK1) - how the heck do i determine which physical hardware device it is that has failed? (without compromising the other data - yes unfortunately I cant afford to backup 11TB of data - personal server). I don't have space in the box for a mouse - not even talking about a hot spare drive - thus adding the backup drive before removing the faulty drive is rather difficult - but if that's the only option I will have to keep with that as everybody know RAID5 is only 1 drive backup - so partly I would like to solve the issue as quick as possible -without having to resort to disconnecting one drive at a time to determine which is which. If the drive assignments ( SDA/SDB/SDC) is constant

What is the most intuitive/fast way to determine that a faulty drive exist in the array? - i.e. is there some sort of GUI solution for MDADM that will tell me the moment that a drive has turned faulty? - The box is currently not on the internet -meaning notification via email is not possible. Is there a non-destructible way to convert the RAID-5 to RAID-6? (I would rather sacrifice 1TB of free space - for peace of mind) - and RAID6 will make troubleshooting a bit easier since 3 drives will have to fail before data-loss.