how to create a degraded raid1 with only 1 of 2 drives ??

how to create a degraded raid1 with only 1 of 2 drives ??

[Mitchell Laks]

Hi mdadm raid gurus,

I wanted to make a raid1 array, but at the moment I have only 1 drive available. The other disk is
in the mail. I wanted to make a raid1 that i will use as a backup.

But I need to do the backup now, before the second drive comes.

So I did this.

formated /dev/sda creating /dev/sda1 with type fd.

then I tried to run
mdadm -C /dev/md0 --level=1 --raid-devices=1 /dev/sda1

but I got an error message
mdadm: 1 is an unusual numner of drives for an array so it is probably a mistake. If you really
mean it you will need to specify --force before setting the number of drives

so then i tried

mdadm -C /dev/md0 --level=1 --force --raid-devices=1 /dev/sda1
mdadm: /dev/sda1 is too small:0K
mdadm: create aborted

now what does that mean?

fdisk -l /dev/sda  shows

device boot	start	end	blocks 	Id	System
/dev/sda1 	1	60801	488384001 fd	linux raid autodetect

so what do I do?


I need to back up my data.
If I simply format /dev/sda1 as an ext3 file system then I can't "add" the second drive later on.

How can I  set it up as a `degraded` raid1 array so I can later on add in the second drive and sync?

Thanks for your help!

Mitchell	

Re: how to create a degraded raid1 with only 1 of 2 drives ??

[michael]

Quoting Mitchell Laks <mlaks@post.harvard.edu>:

> Hi mdadm raid gurus,
>
> I wanted to make a raid1 array, but at the moment I have only 1   
> drive available. The other disk is
> in the mail. I wanted to make a raid1 that i will use as a backup.
>
> But I need to do the backup now, before the second drive comes.
>
> So I did this.
>
> formated /dev/sda creating /dev/sda1 with type fd.
>
> then I tried to run
> mdadm -C /dev/md0 --level=1 --raid-devices=1 /dev/sda1

Perhaps give this a try:

# mdadm -C /dev/md0 --level=1 --raid-devices=2 /dev/sda1 missing

Cheers,
Mike

Re: how to create a degraded raid1 with only 1 of 2 drives ??

[Mitchell Laks]

I think my error was that maybe I did not
do write the fdisk changes to the drive with 
fdisk w

so I did
fdisk /dev/sda
p
then 
w
and then when I did

mdadm -C /dev/md0 --level=2 -n2 /dev/sda1 missing

it worked and set up the array.

Thanks for being there!

Mitchell

Re: how to create a degraded raid1 with only 1 of 2 drives ??

[David Greaves]

Mitchell Laks wrote:
> I think my error was that maybe I did not
> do write the fdisk changes to the drive with 
> fdisk w

No - your problem was that you needed to use the literal word "missing"
like you did this time:
> mdadm -C /dev/md0 --level=2 -n2 /dev/sda1 missing

[however, this time you also asked for a RAID2 (--level=2) which I doubt would work]

David

Re: how to create a degraded raid1 with only 1 of 2 drives ??

[Bill Davidsen]

Mitchell Laks wrote:
> Hi mdadm raid gurus,
>
> I wanted to make a raid1 array, but at the moment I have only 1 drive available. The other disk is
> in the mail. I wanted to make a raid1 that i will use as a backup.
>
> But I need to do the backup now, before the second drive comes.
>
> So I did this.
>
> formated /dev/sda creating /dev/sda1 with type fd.
>
> then I tried to run
> mdadm -C /dev/md0 --level=1 --raid-devices=1 /dev/sda1
>
> but I got an error message
> mdadm: 1 is an unusual numner of drives for an array so it is probably a mistake. If you really
> mean it you will need to specify --force before setting the number of drives
>
> so then i tried
>
> mdadm -C /dev/md0 --level=1 --force --raid-devices=1 /dev/sda1
> mdadm: /dev/sda1 is too small:0K
> mdadm: create aborted
>
> now what does that mean?
>
> fdisk -l /dev/sda  shows
>
> device boot	start	end	blocks 	Id	System
> /dev/sda1 	1	60801	488384001 fd	linux raid autodetect
>
> so what do I do?
>
>
> I need to back up my data.
> If I simply format /dev/sda1 as an ext3 file system then I can't "add" the second drive later on.
>
> How can I  set it up as a `degraded` raid1 array so I can later on add in the second drive and sync?
>   

Specify two drives and one as missing.

-- 
Bill Davidsen <davidsen@tmr.com>
  "Woe unto the statesman who makes war without a reason that will still
  be valid when the war is over..." Otto von Bismark