Re: Migrating from SINGLE DISK to RAID1

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  
[off-list ref] 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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