[linux-lvm] LVM and *bad* performance (no striping)
Urs Thuermann
urs at isnogud.escape.de
Mon Feb 26 15:44:34 UTC 2001
I tried to use LVM today using Linux 2.4.2 and it mostly works like I
expected. But the performance is unacceptably bad:
isnogud:/root# fdisk -l /dev/sda|grep sda5
/dev/sda5 80 399 2570368+ 8e Linux LVM
isnogud:/root# pvcreate /dev/sda5
pvcreate -- physical volume "/dev/sda5" successfully created
isnogud:/root# vgcreate vg0 /dev/sda5
vgcreate -- INFO: using default physical extent size 4 MB
vgcreate -- INFO: maximum logical volume size is 255.99 Gigabyte
vgcreate -- doing automatic backup of volume group "vg0"
vgcreate -- volume group "vg0" successfully created and activated
isnogud:/root# lvcreate -n test /dev/vg0 -L 300M
lvcreate -- doing automatic backup of "vg0"
lvcreate -- logical volume "/dev/vg0/test" successfully created
isnogud:/root# time dd if=/dev/sda5 of=/dev/null count=100000
100000+0 records in
100000+0 records out
real 0m6.720s
user 0m0.300s
sys 0m0.970s
isnogud:/root# time dd if=/dev/vg0/test of=/dev/null count=100000
100000+0 records in
100000+0 records out
real 0m41.851s
user 0m0.350s
sys 0m2.250s
When making an ext2 filesystem on /dev/sda5 or /dev/vg0/test
respectivley, the performance of cp'ing, grep'ing all files and rm'ing
all files, seems to be comparable. But why is the performance of
reading the block device with dd so bad?
urs
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