> On Sun, 16 Sep 2012, Todd And Margo Chester wrote:
>
>> On 09/10/2012 12:41 PM, Jeff Siddall wrote:
>>> On 09/10/2012 02:52 PM, Todd And Margo Chester wrote:
>>>> On 09/10/2012 10:05 AM, Jeff Siddall wrote:
>>>>> ME software RAID1 is very reliable
>>>>
>>>> Have you had a software RAID failure? What was the alert?
>>>> And, what did you have to do to repair it?
>>>
>>> Never had a "software" failure.  I have had [too] many hardware
>>> failures, and those show up with the standard MD email alerts (example
>>> attached below).
>>>
>>> Jeff
>>>
>>> ----------
>>>
>>> This is an automatically generated mail message from mdadm
>>>
>>> A DegradedArray event had been detected on md device /dev/md1.
>>>
>>> Faithfully yours, etc.
>>>
>>> P.S. The /proc/mdstat file currently contains the following:
>>>
>>> Personalities : [raid1] [raid6] [raid5] [raid4]
>>> md3 : active raid1 sda5[0]
>>>        371727936 blocks [2/1] [U_]
>>>
>>> md0 : active raid1 sda1[0]
>>>        104320 blocks [2/1] [U_]
>>>
>>> md2 : active raid1 sda3[0]
>>>        2096384 blocks [2/1] [U_]
>>>
>>> md1 : active raid1 sda2[0]
>>>        16779776 blocks [2/1] [U_]
>>>
>>> unused devices: <none>
>>>
>>
>> Hi Jeff,
>>
>>   Thank you.
>>
>>   I do not understand what I am looking at.  All four
>> entries are RAID1, meaning two drives in the array.
>> But what two drives go together?
>>
>>   What does the "[U_]" stand for?  Up?  Should
>> md1 be [D_] for down?
>>
>>   What does [2/1] stand for?
>>
>>   And, just out of curiosity, is it possible to have
>> a hot spare with the above arrangement?
>>
>> -T

On 09/17/2012 12:22 AM, Steven J. Yellin wrote:>      I believe that 
this is the interpretation of /proc/mdstat:
 > Consider, for example,
 >
 >   md2 : active raid1 sda3[0]
 >          2096384 blocks [2/1] [U_]
 >
 > The device is /dev/md2.  It is raid1, meaning partitions on two disk
 > drives mirror each other.  One of the two is /dev/sda3; the other isn't
 > given because something went wrong, but I'll guess it would be /dev/sdb3
 > if sdb were working, and you would also have in the md2 line an
 > identification of the second participant in the mirror, "sdb3[1]".  The
 > mirrored partitions have 2096384 blocks, which I think means about 2 GB.
 > The "[2/1]" means there should be 2 disks in md2, but there is actually
 > 1. The "[U_]" would be "[UU]" if md2 were in perfect working order, but
 > the second drive in md2 is absent.  Perhaps "U" stands for "up", or for
 > "available" in some language other than English.
 >      You can have a hot spare.  If the md2 line read
 >   md2 : active raid1 sdc3[2] sdb3[1] sda3[0]
 >   then the mirror would still consist of sda3 and sdb3.  You can tell
 > sdc3 is the spare because of its "[2]"; only [0] and [1] are needed for
 > successful mirroring.
 >
 > Steven Yellin
 >


Hi Steven,

   Thank you!

It looks like in the example that all four drives are in their
own RAID1 arrays, but are missing their companion drives.
A misconfiguration perhaps?

-T