From mboxrd@z Thu Jan 1 00:00:00 1970 From: Pascal Nobus Subject: Raid MBR Date: Fri, 17 Sep 2010 10:12:51 +0200 Message-ID: <4C932303.5010706@nobus.be> Mime-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit Return-path: Sender: linux-raid-owner@vger.kernel.org To: linux-raid@vger.kernel.org List-Id: linux-raid.ids After some succesfull and some not succesfull recovery's from Raid-1 rashes, I finally want to understand the whole raid/mbr/lilo thing. In the last 3 days I read so many page's about raid lilo mbr that my head is going to explode. So I'll ask my questions here: We normally use this OS: Slackware (10.1 - 13.0) Disks SATA (hot swappable Supermicro) Raid Raid-1 configured manually in /etc/raidtab Bootlader: LILO looks like this boot = /dev/md0 raid-extra-boot = mbr image = /boot/vmlinuz root = /dev/md0 Assumptions (please correct me if I'm wrong) -Bios looks voor bootable media (order can be changed in Bios) -The Bios names this disk 0x80, later on the kernel says it's sda (or da). -Bios will see in sector 0x80 the partitioning of the disk, and will mount the first bootable Primary Partition. And now the Questions: Q: when I do a lilo -v, 3 MBR's got updated (/dev/md0 /dev/sda /dev/sdb) Is this all the same data? In /boot I can see boot.0800 boot.0810 and boot.0900. It is not the same (used diff for that), so I presume I may not change the boot-order in the bios, or not swap disks physicaly? Q: when boot = /dev/md0, will BIOS read from /dev/md0 (then how does it know from which devices it is assembled), or does it not look at /dev/md0 and just uses the first bootable primary partition (/dev/sda1) Q: /dev/md0 is made of /dev/sda1 and /dev/sdb2, and sda breaks. Now you pullout the broken disk and reboot. Now the good disk (sdb) will become sda, but it won't boot because the root-partition is not found on /dev/sda1 (it's on the second one with this disk) Q: If I would throw away /dev/md2, (unmount it, and remove it from /etc/raidtab), it is not possible to re-assmeble /dev/md2 from another partition of that drive, I have to use a never used one before (/dev/md4). Where is this info stored (superblock?) Q: For being totaly safe I need to - put the boot partition from both disk always at the same place (sda1/sdb1 or sda2/sdb2 or sda3/sdb3) - use this option boot = /dev/md0, raid-extra-boot = mbr - never physicaly swap disks, or change boot-order in BIOS - when one disks breaks, replace it by an empty one, partition it, then restore the raid (raidhotadd), do lilo -v, reboot. Q: Is there a real benefit of using mdadm.conf over raidtab.conf? Thanks in advance! Pascal