In order to test Multipath in d-i you still need a patched grub (#442382) but see below.
D-I Multipath Testing
To enable multipath support during installation use
install disk-detect/multipath/enable=true
at the installer prompt. If multipath devices are found these will show up as /dev/mapper/mpath<X> during installation.
Installing Grub Legacy
Since neither Debian's grub nor grub2 support multipath device names yet (483971), you have to manually install a patched grub legacy during installation. A prebuilt deb for i386 is available here. (In case you need to built for another architecture, the sources are available via this git tree).
Method 1
Proseed with the installation until the installer asks you if you want to install grub on the multipath device then:
- switch to the second VT using CTRL-ALT-F2.
- copy the patched grub to /target/tmp
- chroot /target dpkg -i /tmp/grub_*.deb
- switch back to the first VT using CTRL-ALT-F1 and continue with the installation.
Method 2
This method works if you're installing via a serial console and can't switch VTs. Finish the installation until you're asked to reboot. Then:
hit cancel and head back to the main menu
- spawn a shell in d-i.
copy the patched grub deb to /target/tmp.
- then do:
chroot /target dpkg -i /tmp/grub*deb echo "(hd0) /dev/mapper/mpath0" > /boot/grub/device.map grub --device-map=/boot/grub/device.map
assuming your root filesystem is the first partition on the first multipath device (/dev/mapper/mpath0-part1) enter at the grub prompt:
root (hd0,0) setup (hd0) quit
- this should complete without errors
close the shell (CTRL-D)
- reboot the system
Multipath Support in Debian Installer:
This needed/needs to be done to support multipathing natively in DebianInstaller:
libaio udeb (#440320) - done
multipath udeb (#440334) - done
kernel-wedge needs to support multipath-modules (#439410) - done
linux-kernel-di-i386 needs to include multipath-modules (#440447) - done
hw-detect: disk-detect.sh needs to pull in /sbin/multipath and the necessary kernel modules. If there are multipath devices we need to also pull in partman-multipath. (#440439) - done
parted: correctly identify multipath devices (#440675) - done
partman-base (#442236) - done:
- needs to skip block devices that are part of a multipath device (part_of_multipath())
- humandev() needs multipath support
- move all helper functions for the other modules to identify multipath devices here
partman-multipath (added to d-i svn) - done:
- mark devices as multipath
- call kpartx to create the partition mappings
grub: correctly detect multipath partitions (#442382) - patch for grub-legacy needs to be updated for grub2
partman-auto: don't skip multipath devices - (#468799) - done
grub-installer needs the same patch as grub's grub-install and furthermore mustn't treat mpath devices as LVM (#468832) - done
- update the installer manual (TBD)
put up a for easy testing - done - you can use the official Lenny RC images