Hard drive weirdness.

[Rashkae]

David Gibb wrote:
>> mdadm is not getting confused by the changing drive letters.  By
>> default, mdadm scans all devices to find members of it's raid array,,
>> but it may need a bit of convincing to start a degraded array if one of
>> the drives is simply missing out of the blue..
> 
> Good to know! But my impression from what you said was that simply
> pulling the drive might not be the greatest idea. I suppose I could
> simulate a failure using one of the software tools, but that somehow
> isn't quite as satisfying to me as seeing the raid array continue
> working without a drive.
> 

It's certainly a valuable test. I would just limit my testing to a test
environment, and be prepared to nuke and recreate the array  (I might do
it myself, I'm suddenly curious to know what would happen if I force an
array to start with a missing drive, then re-introduce the drive.. I
honestly have no idea.)

> Another thing I was hoping to find out is which physical sata drive is
> sda and which physical drive is sdb. When mdadm tells me /dev/sda has
> failed, for example, I'd really like to replace the right drive.

Check your /dev/disk/by-id directory :) That gives you drive model *and*
serial number.  you can combine with -l to see what /dev/sd? they are
mapped to. (And indeed, Hard drive manufacturers have the courtesy of
printing the same modem/serial numbers on the sticker as they programmed
in the EEPROM, so it's all good.)

You can also query the drive serial number with hdparm -I /dev/sda