Attempting to add a disk to mirror an LVM volume on CentOS 7 always fails with "Insufficient free space: 1 extents needed, but only 0 available". Having searched for a solution, I have tried specifying disks, multiple logging options, adding 3rd log partition, but have not found a solution

Not sure if I am making a rookie mistake, or there is something more subtle wrong (I am more familiar with ZFS, new to using LVM):

# lvconvert -m1 centos_bi/home
  Insufficient free space: 1 extents needed, but only 0 available  
# lvconvert -m1 --corelog centos_bi/home
  Insufficient free space: 1 extents needed, but only 0 available
# lvconvert -m1 --corelog --alloc anywhere centos_bi/home
  Insufficient free space: 1 extents needed, but only 0 available
# lvconvert -m1 --mirrorlog mirrored --alloc anywhere centos_bi/home /dev/sda2
  Insufficient free space: 1 extents needed, but only 0 available  
# lvconvert -m1 --corelog --alloc anywhere centos_bi/home /dev/sdi2 /dev/sda2
  Insufficient free space: 1 extents needed, but only 0 available

The two disks are of the same size, and have identical partition layouts via "sfdisk -d /dev/sdi > part_table; sfdisk /dev/sda < part_table". The current configuration is detailed below.

# pvs
  PV         VG        Fmt  Attr PSize   PFree
  /dev/sda1  centos_bi lvm2 a--  496.00m 496.00m
  /dev/sda2  centos_bi lvm2 a--  465.27g 465.27g
  /dev/sdi2  centos_bi lvm2 a--  465.27g      0

# vgs
  VG        #PV #LV #SN Attr   VSize   VFree
  centos_bi   3   3   0 wz--n- 931.02g 465.75g 

# lvs -a -o +devices
  LV   VG        Attr       LSize   Pool Origin Data%  Move Log Cpy%Sync Convert Devices
  home centos_bi -wi-ao---- 391.64g                                              /dev/sdi2(6050)
  root centos_bi -wi-ao----  50.00g                                              /dev/sdi2(106309)
  swap centos_bi -wi-ao----  23.63g                                              /dev/sdi2(0)


# pvdisplay
  --- Physical volume ---
  PV Name               /dev/sdi2
  VG Name               centos_bi
  PV Size               465.27 GiB / not usable 3.00 MiB
  Allocatable           yes (but full)
  PE Size               4.00 MiB
  Total PE              119109
  Free PE               0
  Allocated PE          119109

  --- Physical volume ---
  PV Name               /dev/sda2
  VG Name               centos_bi
  PV Size               465.27 GiB / not usable 3.00 MiB
  Allocatable           yes
  PE Size               4.00 MiB
  Total PE              119109
  Free PE               119109
  Allocated PE          0

  --- Physical volume ---
  PV Name               /dev/sda1
  VG Name               centos_bi
  PV Size               500.00 MiB / not usable 4.00 MiB
  Allocatable           yes
  PE Size               4.00 MiB
  Total PE              124
  Free PE               124
  Allocated PE          0

# vgdisplay
  --- Volume group ---
  VG Name               centos_bi
  System ID
  Format                lvm2
  Metadata Areas        3
  Metadata Sequence No  10
  VG Access             read/write
  VG Status             resizable
  MAX LV                0
  Cur LV                3
  Open LV               3
  Max PV                0
  Cur PV                3
  Act PV                3
  VG Size               931.02 GiB
  PE Size               4.00 MiB
  Total PE              238342
  Alloc PE / Size       119109 / 465.27 GiB
  Free  PE / Size       119233 / 465.75 GiB

# lvdisplay
  --- Logical volume ---
  LV Path                /dev/centos_bi/swap
  LV Name                swap
  VG Name                centos_bi
  LV Write Access        read/write
  LV Creation host, time localhost, 2014-08-07 16:34:34 -0400
  LV Status              available
  # open                 2
  LV Size                23.63 GiB
  Current LE             6050
  Segments               1
  Allocation             inherit
  Read ahead sectors     auto
  - currently set to     256
  Block device           253:1

  --- Logical volume ---
  LV Path                /dev/centos_bi/home
  LV Name                home
  VG Name                centos_bi
  LV Write Access        read/write
  LV Creation host, time localhost, 2014-08-07 16:34:35 -0400
  LV Status              available
  # open                 1
  LV Size                391.64 GiB
  Current LE             100259
  Segments               1
  Allocation             inherit
  Read ahead sectors     auto
  - currently set to     256
  Block device           253:2

  --- Logical volume ---
  LV Path                /dev/centos_bi/root
  LV Name                root
  VG Name                centos_bi
  LV Write Access        read/write
  LV Creation host, time localhost, 2014-08-07 16:34:37 -0400
  LV Status              available
  # open                 1
  LV Size                50.00 GiB
  Current LE             12800
  Segments               1
  Allocation             inherit
  Read ahead sectors     auto
  - currently set to     256
  Block device           253:0