Note: "permalinks" may not be as permanent as we would like,
direct links of old sources may well be a few messages off.
Is this dual-ROOT scheme below workable? Let me explain using Machine A and Machine B: Machine A - has a stock, ext4, bootable ROOT file system, non-DRBD - has a second ROOT partition that is an RSYNC copy of Machine B - has an ext4 data-only partition, DRBD primary, that uses Machine B as DRBD secondary Machine B - has a stock, ext4, bootable ROOT file system, non-DRBD - has a second ROOT partition that is an RSYNC copy of Machine A - has a (hidden) data-only partition that is DRBD secondary, with Machine A as DRBD primary. (Hidden, because you can only mount ext4 on one machine, not two.) Machine A does an RSYNC of its ROOT partition to the corresponding spare ROOT partition on Machine B regularly, and vice-versa. When Machine A fails, reboot the Machine B hardware (DRBD secondary) using the RSYNC copy of Machine A's ROOT partition. This brings the machine up solo as if it were Machine A, accessing the local DRBD partition as if it were Machine A (DRBD primary). (Perhaps some fsck will be needed to make the ext4 on the DRBD usable?) Is this doable? (I know it works, since I've tried it, but I'm wondering if I'm missing anything.) Work continues using Machine B's hardware, booted to be Machine A (DRBD primary). This is now the new Machine A (DRBD primary), running without any Machine B (DRBD secondary). Repair the failed old Machine A. Boot the old Machine A hardware using the copy of Machine B's ROOT partition. This brings the machine up as if it were Machine B, partnering with the new Machine A to provide secondary DRBD for the data-only partition. This is now the new Machine B (DRBD secondary). It it okay to bring up Machine B's secondary DRBD as primary, simply by using the copy of the ROOT from Machine A? It it okay to make Machine A behave as Machine B, simply by using a copy of Machine B's ROOT? One "gotcha" I've found is that booting Machine A's ROOT on Machine B's hardware leads to mis-numbering of the Machine B network cards as eth2 and eth3 due to Machine A entries already existing in /etc/udev/rules.d/70-persistent-net.rules. I'll have to tweak those at boot time, or perhaps I can create a merged file that works correctly on both machines. -- | Ian! D. Allen - idallen at idallen.ca - Ottawa, Ontario, Canada | Home Page: http://idallen.com/ Contact Improv: http://contactimprov.ca/ | College professor (Free/Libre GNU+Linux) at: http://teaching.idallen.com/ | Defend digital freedom: http://eff.org/ and have fun: http://fools.ca/