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Old 10-26-2013, 09:57 AM   #1
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raid1 boot Why does it work?

I am happy with my bootable raid1 debian with 2 partitions / and swap, by why is it woorking?
If I understand it correctly the MBR starts and then access the /boot directory and starts the booting of the OS.
But how is that possible? Does MBR includes filesystem handling? Impossible MBR is only 512 bytes long.
How can the computer start the loading of an OS before the filesystem is mounted?
Old 10-26-2013, 10:17 AM   #2
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Without knowing what bootloader you are using, I have to speak very generally, but the stage1 bootloader in the MBR is very primitive. It is given, at the time it is installed, the absolute disk addresses of the next stage bootloader, which includes handling for at least one filesystem. Often that next stage bootloader is located in the unpartitioned space that immediately follows the MBR so that it does not move when filesystems are updated. That intermediate bootloader, working with the filesystem that it understands, loads the final bootloader, which implements all of the user-visible features and loads the actual kernel, initramfs, etc.

Note that the above is very general, and is probably not entirely correct for any actual bootloader.
Old 10-26-2013, 11:40 AM   #3
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I would guess that since the disks are mirrored each contains a perfectly valid boot sector so the system BIOS just has to point to one and the system will boot?


mbr, raid

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