Re: Migrating from SINGLE DISK to RAID1

["berk walker" <berk@panix.com>]

I seem to remember that one can create a degraded array.  Then copy over,  
and shoot the old disk and add it to the aray.
b-

On Tue, 01 Feb 2005 20:01:12 +0100, Robert Heinzmann  
<Robert.Heinzmann@gmx.net> wrote:

> Hello,
>
> can someone verify if the following statements are true ?
>
> - It's not possible to simply  convert a existing partition with a  
> filesystem on it to a raid1 mirror set.
>
> This may seem succesfull (filesystem can be mounted and must not be  
> checked), but it will cause data integrity problems. One of the last  
> Blocks of the device formaly used for file data will be used for the  
> raid superblock and so all data on this block will be not accessible  
> anymore.
>
> - Using a former disk of a raid1 array as a usual disk (not mounted as  
> degrated /dev/mdX, but instead mounted as /dev/sdX or /dev/hdX) is  
> successfull.
>
> This is because the MD device layer reports the device size as size of  
> disk - superblock offset during the creation of a filesystem on the MD  
> device. Thus the used size of the disk, when mounting it as /dev/sdX  
> /dev/hdX, is some KB smaller than it could be, but no data is lost.
>
> - Its always possible to use raid1 disks as regular disks (not taking  
> the md autodiscovery into concern). Using regular disks as raid disks  
> always requires data migration (new filesystem and copy).
>
> Thank you very much. I would really appreshiate some somments on this  
> one.
>
> Robert Heinzmann
> -
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