info about hdds in raid

Leonard Chatagnier lenc5570 at
Tue Nov 3 01:25:09 UTC 2009

--- On Mon, 11/2/09, Christopher Chan <christopher.chan at> wrote:

From: Christopher Chan <christopher.chan at>
Subject: Re: info about hdds in raid
To: "Ubuntu user technical support, not for general discussions" <ubuntu-users at>
Date: Monday, November 2, 2009, 6:31 PM

>> How can I tell wich HDD to swap, when the "cat
>> /proc/mdstat" says one HDD of the RAID1 array has
>> died?
> I read this with interest but I don't see where the commands would show which drive has failed.  Is is something obvious to you that isn't to me, someone who has never used any raid setup. I certainly would like to know as I have a computer in my lan with 2 HDDs that someday when I'm feeling reckless may try to set up a raid system.
> Leonard Chatagnier
> lenc5570 at
 cat /proc/mdstat
Personalities : [linear] [multipath] [raid0] [raid1] [raid6] [raid5] 
[raid4] [raid10]
md1 : active raid1 sda2[0] sdb2[1]
      243954944 blocks [2/2] [UU]
md0 : active raid1 sda1[0] sdb1[1]
      240832 blocks [2/2] [UU]
unused devices: <none>

The UU in square brackets tell us that all disks are Up. If you see a 
'_', then that disk/partition is down/dropped. So if I had

md0 : active raid1 sda1[0] sdb1[1]
      240832 blocks [2/2] [U_]

then that means that sdb1 needs some work done.

Thanks so much for the info.  I've learned something new today and will file this away for future reference.  Thanks again.  

Leonard Chatagnier

lenc5570 at

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