Making space for another OS.

[Bill Rugolsky Jr.]

On Tue, Nov 15, 2005 at 03:50:00PM +0000, Craig McLean wrote:
> Gotcha. Hopefully once the filesystem is resized down and the lvreduce
> is done, moving the physical partition boundary will not destroy any
> allocated PEs, good call on the vgcfgbackup/restore. I wouldn't know
> where to start working out the new PE count for the restore though...
> Will vgdisplay show me the new PE count after the resize?

Use "lvdisplay -m" to get a map of the segments; e.g., one of my logical
volumes shows:

  --- Logical volume ---
  LV Name                /dev/extra/extra_disk
  VG Name                extra
  LV UUID                cTvMfD-XTIT-NQhs-vsnO-sgDq-ltXA-jVf0Pg
  LV Write Access        read/write
  LV Status              available
  # open                 1
  LV Size                56.00 GB
  Current LE             56
  Segments               2
  Allocation             inherit
  Read ahead sectors     0
  Block device           253:1
   
  --- Segments ---
  Logical extent 0 to 7:
    Type                linear
    Physical volume     /dev/md7
    Physical extents    130 to 137
   
  Logical extent 8 to 55:
    Type                linear
    Physical volume     /dev/md7
    Physical extents    144 to 191

 
This corresponds to the following metadata in the backup file created by
vgcfgbackup; I've elided the other logical volumes for brevity:

extra {
        id = "vh30BJ-06Yt-uJTS-O5S4-ZyZc-r9vQ-Hfd7IU"
        seqno = 7
        status = ["RESIZEABLE", "READ", "WRITE"]
        extent_size = 2097152           # 1024 Megabytes
        max_lv = 0
        max_pv = 0

        physical_volumes {

                pv0 {
                        id = "jNBJ7Y-wZ4r-IPyn-KLkP-xjdU-NRXu-f2yUBu"
                        device = "/dev/md7"     # Hint only

                        status = ["ALLOCATABLE"]
                        pe_start = 384
                        pe_count = 224  # 224 Gigabytes
                }
        }

        logical_volumes {

                extra_disk {
                        id = "cTvMfD-XTIT-NQhs-vsnO-sgDq-ltXA-jVf0Pg"
                        status = ["READ", "WRITE", "VISIBLE"]
                        segment_count = 2

                        segment1 {
                                start_extent = 0
                                extent_count = 8        # 8 Gigabytes

                                type = "striped"
                                stripe_count = 1        # linear

                                stripes = [
                                        "pv0", 130
                                ]
                        }
                        segment2 {
                                start_extent = 8
                                extent_count = 48       # 48 Gigabytes

                                type = "striped"
                                stripe_count = 1        # linear

                                stripes = [
                                        "pv0", 144
                                ]
                        }
                }
	}
}

So to hack this up manually, you'd have to first verify that no segment extends
beyond the new end of the physical volume, and then reduce the pe_count in
the meta-data.

Best of luck,

	Bill Rugolsky