• FeatureRequests
• external
• Booting

Requirements

• boot from any hard disk/PV
• boot when disks are missing

Prerequisites

• mirroring over an arbitrary number of copies; RAID(n,n-1).

• fault-tolerant mirroring.

• FeatureRequests/defrag

• changes to GRUB2

Details

An LV is bootable, if it has a contiguous copy at the beginning of every PV marked as bootable. An LV is marked as bootable if the user requested that the LV be bootable. On a Linux system, usually /boot would be marked as bootable.

A PV is bootable if it has a contiguous copy of the bootable LV at its beginning. An PV is marked as bootable if the user requested that the PV be bootable. By default, the first PV on a disk drive that belongs to a VG is marked as bootable.

A VG is bootable if it has at least one bootable PV. A VG is marked as bootable if it has a LV marked as bootable.

LVM user space tools will try to ensure that every LV/PV marked as bootable becomes and remains bootable:

• On a PV marked as bootable, tools will not allocate space at the beginning (unless --force'd)
• When a PV is marked as bootable, tools will automatically create a degraded copy of the LV marked as bootable on it.
• When a LV is marked as bootable, tools will automatically create a degraded copy of it on every PV marked as bootable.
• When enough space at the beginning of a PV is deallocated (pvmove, lvdelete), tools will automatically create a degraded copy of the LV marked as bootable if it's missing.
• The hypothetic VG re-organiser (defrag) will automatically try to make room at the beginning.
• lvchange will refuse to enlarge a bootable LV if there's not enough room on every bootable PV.

Making a VG bootable could be done like this:

•  # lvcreate --boot y -L 100M -n boot acme
   …
   WARNING: Not enough room to make /dev/sda2 bootable.
   WARNING: Not enough room to make /dev/sdb1 bootable.
   WARNING: Not enough room to make /dev/sdc1 bootable.
   WARNING: Not enough room to make /dev/sdd1 bootable.
   WARNING: There are no bootable PVs in VG acme.

   # pvs
   
   PV         VG    Fmt  Attr PSize   PFree  
   /dev/sda2        lvm2 --B  200,00G   5,00G
   /dev/sdb1        lvm2 --B  100,00G   0,00G
   /dev/sdb2        lvm2 ---  100,00G   2,00G
   /dev/sdc1        lvm2 --B  200,00G   0,00G
   /dev/sdd1        lvm2 --B  100,00G   3,00G
   /dev/sdd2        lvm2 ---  100,00G   0,00G

  (NB: B denotes marked as bootable but not bootable)

   # pvmove --defrag --quick
   
   …

   # pvs
   
   PV         VG    Fmt  Attr PSize   PFree  
   /dev/sda2        lvm2 --b  200,00G   4,80G
   /dev/sdb1        lvm2 --b  100,00G   0,00G
   /dev/sdb2        lvm2 ---  100,00G   2,00G
   /dev/sdc1        lvm2 --b  200,00G   0,00G
   /dev/sdd1        lvm2 --b  100,00G   2,90G
   /dev/sdd2        lvm2 ---  100,00G   0,00G

  (NB: b denotes bootable)

   # mkfs … /dev/boot/acme
  
   # mount /dev/boot/acme /mnt
  
   # cp -av /boot /mnt
  
   # $EDITOR /dev/fstab
  
   # grub2-install /dev/boot/acme