deliberately degrading RAID1 to a single disk, then back again

deliberately degrading RAID1 to a single disk, then back again

[Maurice Hilarius]

Good day all.

Scenario:
Pair of identical disks.
partitions:
Disk 0:
/boot - NON-RAIDed
swap
/  - rest of disk

Disk 01
/boot1 - placeholder to take same space as /boot on disk0 - NON-RAIDed
swap
/  - rest of disk

I created RAID1 over / on both disks, made /dev/md0

From time to time I want to "degrade" back to only single disk, and turn
off RAID as the overhead has some cost
From time to time I want to restore to RAID1 function, and re-synch the
pair to current.

Yes, this is a backup scenario..

Are there any Recommendations ( with mdadm syntax)  please?





-- 

-- 

Regards,
	Maurice
09 F9 11 02 9D 74 E3 5B D8 41 56 C5 63 56 88 C0

1001 11111001 00010001 00000010 10011101 01110100 11100011 01011011 11011000 01000001 01010110 11000101 01100011 01010110 10001000 11000000

10 base 13,256,278,887,989,457,651,018,865,901,401,704,640 

Re: deliberately degrading RAID1 to a single disk, then back again

[Justin Piszcz]

mdadm /dev/md0 --fail /dev/sda1

On Tue, 26 Jun 2007, Maurice Hilarius wrote:

> Good day all.
>
> Scenario:
> Pair of identical disks.
> partitions:
> Disk 0:
> /boot - NON-RAIDed
> swap
> /  - rest of disk
>
> Disk 01
> /boot1 - placeholder to take same space as /boot on disk0 - NON-RAIDed
> swap
> /  - rest of disk
>
> I created RAID1 over / on both disks, made /dev/md0
>
>> From time to time I want to "degrade" back to only single disk, and turn
> off RAID as the overhead has some cost
>> From time to time I want to restore to RAID1 function, and re-synch the
> pair to current.
>
> Yes, this is a backup scenario..
>
> Are there any Recommendations ( with mdadm syntax)  please?
>
>
>
>
>
> -- 
>
> -- 
>
> Regards,
> 	Maurice
> 09 F9 11 02 9D 74 E3 5B D8 41 56 C5 63 56 88 C0
>
> 1001 11111001 00010001 00000010 10011101 01110100 11100011 01011011 11011000 01000001 01010110 11000101 01100011 01010110 10001000 11000000
>
> 10 base 13,256,278,887,989,457,651,018,865,901,401,704,640
>
>
> -
> To unsubscribe from this list: send the line "unsubscribe linux-raid" in
> the body of a message to majordomo@vger.kernel.org
> More majordomo info at  http://vger.kernel.org/majordomo-info.html
>

Re: deliberately degrading RAID1 to a single disk, then back again

[Mike Accetta]

Justin Piszcz wrote:
> mdadm /dev/md0 --fail /dev/sda1
> 
> On Tue, 26 Jun 2007, Maurice Hilarius wrote:
> 
...
>>> From time to time I want to "degrade" back to only single disk, and turn
>> off RAID as the overhead has some cost
>>> From time to time I want to restore to RAID1 function, and re-synch the
>> pair to current.
>>
>> Yes, this is a backup scenario..
>>
>> Are there any Recommendations ( with mdadm syntax)  please?

Plus

   mdadm /dev/md0 --remove /dev/sda1

to take the drive out of the array and

   mdadm /dev/md0 --add /dev/sda1

to put it back and start the re-sync.

When you mention "turn off RAID" do you mean to not even bring up the disk
as a degraded array?  If all you do is fail and remove the partition, RAID is
actually still running to manage the single remaining partition, but I would
expect that overhead to be minimal.
-- 
Mike Accetta

ECI Telecom Ltd.
Transport Networking Division, US (previously Laurel Networks)