[linux-lvm] Testing the new LVM cache feature

[Richard W.M. Jones]

It works once I use a single VG.

However the performance is exactly the same as the backing hard disk,
not the SDD.  It seems I'm getting no benefit ...

# lvs
[...]
  testoriginlv           vg_guests Cwi-a-C--- 100.00g lv_cache [testoriginlv_corig]                                 

# mount /dev/vg_guests/testoriginlv /tmp/mnt
# cd /tmp/mnt

# dd if=/dev/zero of=test.file bs=64K count=100000 oflag=direct
100000+0 records in
100000+0 records out
6553600000 bytes (6.6 GB) copied, 57.6301 s, 114 MB/s

# dd if=test.file of=/dev/zero bs=64K iflag=direct
100000+0 records in
100000+0 records out
6553600000 bytes (6.6 GB) copied, 47.6587 s, 138 MB/s

(Exactly the same numbers as when I tested the underlying HDD, and
about half the performance of the SDD.)

Rich.

-- 
Richard Jones, Virtualization Group, Red Hat http://people.redhat.com/~rjones
Read my programming and virtualization blog: http://rwmj.wordpress.com
virt-builder quickly builds VMs from scratch
http://libguestfs.org/virt-builder.1.html