Comment # 6 on bug 1172566 from heming zhao

in my kvm-qemu, 2 1000g scsi disks, still can't reproduction.

```
tb-base40g:~ # pvcreate /dev/sdb
  Physical volume "/dev/sdb" successfully created.
tb-base40g:~ # pvcreate /dev/sda
  Physical volume "/dev/sda" successfully created.
tb-base40g:~ # vgcreate test /dev/sdb /dev/sda
  Volume group "test" successfully created
tb-base40g:~ # lsblk
NAME   MAJ:MIN RM  SIZE RO TYPE MOUNTPOINT
sda      8:0    0 1000G  0 disk 
sdb      8:16   0 1000G  0 disk 
sr0     11:0    1  4.3G  0 rom  
vda    253:0    0   40G  0 disk 
������vda1 253:1    0    8M  0 part 
������vda2 253:2    0   38G  0 part /
������vda3 253:3    0    2G  0 part [SWAP]
vdb    253:16   0    1G  0 disk 
������vdb1 253:17   0 1023M  0 part 
vdc    253:32   0    1G  0 disk 
������vdc1 253:33   0 1023M  0 part 
tb-base40g:~ # lvcreate --size 512g --name giant test /dev/sda
  Logical volume "giant" created.
tb-base40g:~ # lvcreate --size 96g --name giant-cache test /dev/sdb
  Logical volume "giant-cache" created.
tb-base40g:~ # lvconvert --type cache --cachevol giant-cache --cachemode
writeback --chunksize 128 test/giant
Erase all existing data on test/giant-cache? [y/n]: y
  WARNING: repairing a damaged cachevol is not yet possible.
  WARNING: cache mode writethrough is suggested for safe operation.
Continue using writeback without repair?y
  Logical volume test/giant is now cached.
tb-base40g:~ # lvconvert --splitcache test/giant
  Flushing 0 blocks for cache test/giant.
  Logical volume test/giant is not cached and test/giant-cache is unused.
tb-base40g:~ # lvresize --size 128g test/giant-cache
  Size of logical volume test/giant-cache changed from 96.00 GiB (24576
extents) to 128.00 GiB (32768 extents).
  Logical volume test/giant-cache successfully resized.
tb-base40g:~ # lvconvert --type cache --cachevol giant-cache --cachemode
writeback --chunksize 256 test/giant
Erase all existing data on test/giant-cache? [y/n]: y
  WARNING: repairing a damaged cachevol is not yet possible.
  WARNING: cache mode writethrough is suggested for safe operation.
Continue using writeback without repair?y
  Logical volume test/giant is now cached.
tb-base40g:~ # lvs -a
  LV                 VG   Attr       LSize   Pool               Origin       
Data%  Meta%  Move Log Cpy%Sync Convert
  giant              test Cwi-a-C--- 512.00g [giant-cache_cvol] [giant_corig]
0.01   14.86           0.00            
  [giant-cache_cvol] test Cwi-aoC--- 128.00g                                    
  [giant_corig]      test owi-aoC--- 512.00g
tb-base40g:~ # rpm -qa | grep lvm2
lvm2-2.03.05-8.1.x86_64
lvm2-testsuite-2.03.05-7.2.x86_64
liblvm2cmd2_03-2.03.05-8.1.x86_64
```