On Sunday September 11, xucs007@xxxxxxxxx wrote: > Thanks for your quick response. > > It won't matter if I want to use 2 blank partitions to build RAID1; > > But now I wish to use mdadm to backup my /home partition, which > already has tons of files on it; You probably don't want to do that. Normally a raid1 array created by mdadm is slightly smaller than the original device, to allow room for some metadata. If you create a raid1 using a device with an existing filesystem, you will probably corrupt that filesystem - though it may be possible to 'resize' it a few hundred Kilobytes smaller first. > > If mdadm happens to choose the other blank partition as source > to do mirroring, all my data on /home will be lost; If this really is something you want to do (e.g. you do shrink the filesystem first, or you use --build to make an array without metadata (not recommended unless you really know what you are doing)), then the thing to do is create the array with only one active device, and one 'missing' device. Thus the data on the active device will have to be the data using in the array. Then you hot-add the drive that you want data to be copied on to. When you hot-add a spare to an array, you can be certain that data will be copied ONTO it, not OFF OF it. However the recommended approach is to create a degraded array using the new drive, make a filesystem there-on, copy the data, and once you are sure the data is safe, add the original drive as a spare to the new array. e.g. assuming sda1 has your /home and sdb1 is the same size: mdadm --create /dev/md1 --level=1 -n2 missing /dev/sdb1 mkfs /dev/md1 mount /dev/md1 /mnt cp -a /home /mnt # convince yourself that the copy was successful umount /mnt umount /home mount /dev/md1 /home # convince yourself again that /home is good mdadm /dev/md1 --add /dev/sda1 # update /etc/fstab and /etc/mdadm.conf as required > > Hardware RAID always allows me to choose which partition/drive > to be used as source. Probably because customers ask for it and hardware manufacturers think it is good to give customers what they want. I prefer to tell customers what they need :-) NeilBrown - To unsubscribe from this list: send the line "unsubscribe linux-raid" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
