> > 1. Add a 3rd Device to the exisiting SoftRaid1. In this method my mdadm > monitor will always sent an error message for the Raid. So it isn´t the > best, I think. >
Why do you think it would show an error? remove the device from the raid with mdadm. Then there is no error. Sure you may see that the array is missing a member but that doesnt really matter and will cause no issues. This is a good method with no apparent downsides. > > 2. Make a snapshot from the filesystem with LVM and copy it with dd to an > external esata drive. But I read about problems with grub?! > maybe you should put your OS on a separate drive from the backuppc $TopDIR. You dont need to LVM snapshot your home directory. You can use the backuppc program to backup the whole os drive and be able to restore it to another drive without issue. For that matter, you can keep a copy of the backuppc configs somewhere and if you do loose the OS drive, you can boot from a livecd like ubuntu, install backuppc and copy the config in and access those files, even the OS files and do a restore on them. You do not need grub in any way for the backuppc data store. What issues would you anticipate with grub? just boot from a live cd and reinstall grub... > > My requirement is that if the two HDDs in the Server fail, I can boot from > the external drive without much work. > consider making your boot disk a raid1 with 2 or more members. Make one of those members a USB flash key. make sure you install grub on all disks in the mirror so you can boot from them as mdadm does not touch the MBR during array creation. I actually run a few servers with the / on mirrored USB flash keys. They are many times more reliable than hard disks as a / drive as very little is written here, mostly reads. Then put /var /home (but not /etc) on a different disk. I put a 2 port USB bracket inside the case so that my flash disks dont get pulled in error. > > My questions are: > - What is the safer method? > - Which method is better for the pool? > - What do you think, which method I should prefer with 3x 1TB HDDs? > I like the mdadm mirror setup. You can then read the partition as is on a linux system. There are some novel tricks that you can do with this. setup a small system in another building or somewhere on the local network and use ATA over Ethernet to export the entire disk, then add this AoE disk to the raid1. Now you can have a mirror of the OS disk. You could also setup a disk somewhere on another network and export the disk over iscsi and add it to the local mirror. It is a good idea to seperate your OS onto a different disk than backuppc uses. If you do this you wont need a lot of bandwidth to maintain the mirror as few writes will happen on the OS. since you dont look like you are trying to do raid5 and just want a tripple redundant 1TB raid1, I suggest mdadm. With a simple array like this you dont even need to do LVM. LVM is just another layer so skip it if you dont need it. since you have at a 3rd disk, you can change this later if you want to add more space, but by that time you may be ready to move up to a bigger setup with some hardware raid5 or something and will likely have other filesystem options like btfs and ext4 that you will probably want to migrate to anyway.
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