Re: [Hampshire] Simple RAID problem

----- Original Message -----
From: "Stuart Sears" <stuart@???>
To: "Hampshire LUG Discussion List" <hampshire@???>
Sent: Saturday, March 28, 2009 4:08 PM
Subject: Re: [Hampshire] Simple RAID problem


> Rob Malpass wrote:
>> Hi all
>>
>> Trying to setup raid (on Ubuntu 8.1) with the command
>>
>> mdadm --assemble /dev/md0 /dev/sdb /dev/sdc
>>
>> and receiving the error no recognisable superblock on /dev/sdb
>>
>> The thing is I can mount both drives having formatted them to ext3
>> previously.
>
> mdadm --assemble is used to reconstruct an existing array, not create a
> new one.
>
> For that you want mdadm --create (or -C for those of us who dislike
> typing for typing's sake)
>
> what kind of RAID array are you trying to configure?
> RAID 1 mirror?
>
> Are you sure you used the entire disk in each case and not individual
> partitions?
>
>> I don't know what superblock means but I thought it meant that the
>> drive's not formatted - which it obviously is if I can mount and
>> read/write to it.
>
> nope, it means that the drive has never been part of a RAID array, which
> it won't have been unless you already set it up :)
>
>> I must be doing something obvious wrong - but can't see what. To
>> the best of my knowledge I've followed the guide at
>
> ** LONG-WINDED RAID INSTRUCTIONS **
[snip]

Brilliant - thanks Hugo and Stuart for your advice. AFAIK I've now setup
raid1 across two devices on a virtual machine. The thing is - how do I
verify this?

As I understand it - everything I now send to /dev/md0 (which I've mounted
under /mnt) is sent to both /dev/sdb and /dev/sdc simultaneously.
Presumably (I've not tried) but it won't just let me mount them somewhere
else so I can see what's going on as they're now part of a raid device and
won't contain ext3 filesystems - is that right?

Thanks again - assuming I can verify it - I'm just the purchase of the
hardware away from a DIY Drobo at a fraction of the cost *


Cheers
Rob

* Yes yes - I know Drobo has some other nice features which I'm not setting
up here.