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

[Dax Kelson]

On Fri, Jul 10, 2015 at 4:53 PM, Dax Kelson <dkelson at gurulabs.com> wrote:
> 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.


Here is the speed going directly against the Cache data LV and the OriginLV.

[root at virthost03 tmp]# echo 1 > /proc/sys/vm/drop_caches
[root at virthost03 tmp]# dd if=/dev/mapper/virthost03-CacheLV_cdata
of=/dev/null count=1 skip=30  bs=1GB
1+0 records in
1+0 records out
1000000000 bytes (1.0 GB) copied, 1.08997 s, 917 MB/s
[root at virthost03 tmp]# echo 1 > /proc/sys/vm/drop_caches
[root at virthost03 tmp]# dd if=/dev/mapper/virthost03-root_corig
of=/dev/null count=1 skip=30  bs=1GB
1+0 records in
1+0 records out
1000000000 bytes (1.0 GB) copied, 1.73674 s, 576 MB/s
[root at virthost03 tmp]#

Reading from the CacheLV is slower than even the OriginLV?!?

[root at virthost03 tmp]# echo 1 > /proc/sys/vm/drop_caches
[root at virthost03 tmp]# dd if=/dev/mapper/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, 6.77021 s, 148 MB/s