- I'm creating a new RAID1 array using mdadm.
I won't be using additional layers, such as LVM or dm-crypt.
I've noticed that metadata version 1.2 is now the default. I understand it's the recommended version, if all other parts of the system (for example grub2) support it. This is the case for me.
- From the manpage and several other sources I understand that metadata 1.2 means the superblock is stored at the beginning of the disk. At 4KiB from the start.
- On previous RAID1 arrays I created, I used metadata version 0.90 which stores the superblock at the end of the disk instead. To prevent it from being overwritten, I left the last part of the disk unpartitioned.
It's my intention to partition the new RAID1 array with a GPT partition table, first partition starting at sector 2048. If a sector is 512 bytes, this means the actual partition will start at 1024KiB from the start of the disk.
- Should I take any precautions to prevent the version 1.2 superblock from being overwritten, or is starting the first partition at sector 2048 enough to be relatively safe?
- I imagine grub will write at the start of the disk, but it will probably only need the first 512 bytes. Do any other programs write right after those bytes on the disk?
- Is the part right after the end of the first sector, up to sector 2048, a 'regulated' part of the disk? Do other programs check if any other data is present before they start writing there? I couldn't find anything specific about this.
I understand that using
dd can destroy a superblock ;-) and so does
mdadm --zero-superblock. I'm more concerned about any other utilities or filesystem layers such as LVM of which I may not immediately realise they could overwrite that specific part of the disk where the superblock is stored.