[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.

[***@virthost03 tmp]# echo 1 > /proc/sys/vm/drop_caches
[***@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
[***@virthost03 tmp]# echo 1 > /proc/sys/vm/drop_caches
[***@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
[***@virthost03 tmp]# echo 1 > /proc/sys/vm/drop_caches
[***@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
[***@virthost03 tmp]# echo 1 > /proc/sys/vm/drop_caches
[***@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
[***@virthost03 tmp]#

Help?

[Dax Kelson]

Post by 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.

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

[***@virthost03 tmp]# echo 1 > /proc/sys/vm/drop_caches
[***@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
[***@virthost03 tmp]# echo 1 > /proc/sys/vm/drop_caches
[***@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
[***@virthost03 tmp]#

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

[***@virthost03 tmp]# echo 1 > /proc/sys/vm/drop_caches
[***@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