[linux-lvm] Trying to see a difference in performance with LVM Cache

[Dax Kelson]

My "root" LV is attached to a LVM Cache Pool that is about 900GB in size.

The Origin/Slow LV can do about 560 MB/sec and the Fast/CacheLV can do
about double that speed.

# lvs
  LV   VG         Attr       LSize   Pool      Origin       Data%
Meta%  Move Log Cpy%Sync Convert
  root virthost03 Cwi-aoC--- 831.94g [CacheLV] [root_corig] 0.06
8.27            0.00
  swap virthost03 -wi-ao----   4.00g

I'm trying see a performance difference, and I would expect these
speeds to increase.

[root at virthost03 tmp]# echo 1 > /proc/sys/vm/drop_caches
[root at virthost03 tmp]# dd if=/dev/virthost03/root of=/dev/null count=1
skip=30  bs=1GB
1+0 records in
1+0 records out
1000000000 bytes (1.0 GB) copied, 5.88505 s, 170 MB/s
[root at virthost03 tmp]# echo 1 > /proc/sys/vm/drop_caches
[root at virthost03 tmp]# dd if=/dev/virthost03/root of=/dev/null count=1
skip=30  bs=1GB
1+0 records in
1+0 records out
1000000000 bytes (1.0 GB) copied, 6.04174 s, 166 MB/s
[root at virthost03 tmp]# echo 1 > /proc/sys/vm/drop_caches
[root at virthost03 tmp]# dd if=/dev/virthost03/root of=/dev/null count=1
skip=30  bs=1GB
1+0 records in
1+0 records out
1000000000 bytes (1.0 GB) copied, 6.27378 s, 159 MB/s
[root at virthost03 tmp]# echo 1 > /proc/sys/vm/drop_caches
[root at virthost03 tmp]# dd if=/dev/virthost03/root of=/dev/null count=1
skip=30  bs=1GB
1+0 records in
1+0 records out
1000000000 bytes (1.0 GB) copied, 8.66593 s, 115 MB/s
[root at virthost03 tmp]#

Help?