#!/bin/sh
msg () { tput setaf 1; echo "$*"; tput op; }

msg ===== Write directly to hard-disk
msg == 1. write block directly to hard-disk
lvcreate -L 4G -n test1 vg_ucs
#   Logical volume "test1" created
echo 1 >/proc/sys/vm/drop_caches
time dd if=/dev/zero bs=1M count=4k conv=fsync oflag=direct of=/dev/vg_ucs/test1
# 4096+0 Datensätze ein
# 4096+0 Datensätze aus
# 4294967296 Bytes (4,3 GB) kopiert, 47,1095 s, 91,2 MB/s
# 
# real    0m47.132s
# user    0m0.004s
# sys     0m4.428s

msg ===== Write to CoW-end
msg == 1. write block directly to hard-disk
msg == 2. update CoW-table and write to disk
lvcreate -s -L 4,1G -n test2 /dev/vg_ucs/test1
#   Rounding up size to full physical extent 4,10 GB
#   Logical volume "test2" created
echo 1 >/proc/sys/vm/drop_caches
time dd if=/dev/zero bs=1M count=4k conv=fsync oflag=direct of=/dev/vg_ucs/test2
# 4096+0 Datensätze ein
# 4096+0 Datensätze aus
# 4294967296 Bytes (4,3 GB) kopiert, 153,322 s, 28,0 MB/s
# 
# real    2m33.330s
# user    0m0.096s
# sys     0m13.125s

msg ===== Write to CoW-end again
msg == 1. write block directly to hard-disk
echo 1 >/proc/sys/vm/drop_caches
time dd if=/dev/zero bs=1M count=4k conv=fsync oflag=direct of=/dev/vg_ucs/test2
# 4096+0 Datensätze ein
# 4096+0 Datensätze aus
# 4294967296 Bytes (4,3 GB) kopiert, 48,3079 s, 88,9 MB/s
# 
# real    0m48.495s
# user    0m0.100s
# sys     0m19.761s

msg ===== Write to origin-end
msg == 1. read original block from origin
msg == 2. write original block to CoW device
msg == 3. update CoW-table and write to disk
msg == 4. write modified block to origin
lvremove -f /dev/vg_ucs/test2
lvcreate -s -L 4,1G -n test3 /dev/vg_ucs/test1
#   Rounding up size to full physical extent 4,10 GB
#   Logical volume "test3" created
echo 1 >/proc/sys/vm/drop_caches
time dd if=/dev/zero bs=1M count=4k conv=fsync oflag=direct of=/dev/vg_ucs/test1
# 4096+0 Datensätze ein
# 4096+0 Datensätze aus
# 4294967296 Bytes (4,3 GB) kopiert, 195,556 s, 22,0 MB/s
# 
# real    3m15.760s
# user    0m0.096s
# sys     0m13.205s

msg ===== Write to origin-end again
msg == 1. write block directly to hard-disk
echo 1 >/proc/sys/vm/drop_caches
time dd if=/dev/zero bs=1M count=4k conv=fsync oflag=direct of=/dev/vg_ucs/test1
# 4096+0 Datensätze ein
# 4096+0 Datensätze aus
# 4294967296 Bytes (4,3 GB) kopiert, 59,0429 s, 72,7 MB/s
# 
# real    0m59.273s
# user    0m0.108s
# sys     0m17.181s

lvremove -f /dev/vg_ucs/test3
lvremove -f /dev/vg_ucs/test1