I'm in a bit of a pickle. I have a headless server (Acer EasyStore) running Ubuntu 12.04.1, which, after an update, now refuses to boot. It has four disks, one of which holds the OS in a partition and the rest, along with the other three disks, is an mdraid array.

I've inserted the OS disk in another computer (a VM) and tried to boot, but it gives me a scary error message:

WARNING: There appears to be one or more degraded RAID devices **                                                   
The system may have suffered a hardware fault, such as a disk drive                                                 
failure.  The root device may depend on the RAID devices being online. One                                          
or more of the following RAID devices are degraded:                                                                 
Personalities : [linear] [multipath] [raid0] [raid1] [raid6] [raid5] [raid4] [raid10]                               

unused devices: <none>                                                                                              
You may attempt to start the system anyway, or stop now and attempt                                                 
manual recovery operations.  To do this automatically in the future,                                                
add "bootdegraded=true" to the kernel boot options.                                                                 

If you choose to start the degraded RAID, the system may boot normally,                                             
but performance may be degraded, and a further hardware fault could                                                 
result in permanent data loss.                                                                                      

If you abort now, you will be provided with a recovery shell.                                                       

Do you wish to start the degraded RAID? [y/N]:

I want to continue and see what's going on (and if the server will start SSH so I can log into it), but this message is really scary. If I boot without the RAID, will I lose all my data? It doesn't stand to reason that I'd lose the array even though all four disks are fine, but the warning is very strongly worded.

Does anyone know if this means I'll lose my data? Is there another alternative?


In the end, I decided to answer "yes" to the prompt. It dropped me in an initramfs shell, I exited it and it resumed booting. It turned out that the kernel I had upgraded was not working properly, but the array was fine, even after I had answered "yes" multiple times with failed boots, even getting to the user prompt (the array was obviously not mounted when the disks weren't present).

So, that message is not too much to worry about.


Generally, it would be safer to answer No and don't try to start the degraded RAID. In this case you would also be given a recovery shell.

You did not post RAID level here. But I think you did not use something like RAID-1 array that consists of 4 disks. So you anyway could not build/recover an array from the disk containing 1/4, 1/2 or 1/3 part of your data.

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