Dne 18. 07. 25 v 14:24 Henry, Andrew napsal(a): >> Maybe you virtual system does have it self 'a single write pipe' - so any >> parallelization is stopped right there - so maybe you should start first >> with bare metal.... > > This is what I suspect is happening, as the back-end storage is very fast. > I'm going to test on a physical server instead. > > /AH
It's crucially important to be sure - you have independent drives & controller paths to them. It's really pointless trying to setup a 'stripe' on top of 3 drives that are at the end served by a singly physical storage behind the scene - this likely can explain rather horrible numbers you get when you are trying to use stripe - in such case simply join devices 1-by-1.... Zdenek I re-tested this on a consumer PC. SATA6 controller, 2 * 1TB Seagate 4ke drives with product spec of ~210MB/s read speed and ~160MB/s write speed. Created the lv as follows: Pvcreate --dataalignmentoffset 7 /dev/sda /dev/sdb Vgcreate vg00 /dev/sda /dev/sdb lvcreate -n swap -l +100%FREE vg00 # for linear lvm lvcreate -n swap -i 2 -I 4k --type=striped -l +100%FREE vg00 # for striped lvm mkfs -t xfs -b size=4K -d su=4k,sw=2 -f /dev/vg00/swap mount /dev/vg00/swap /mnt Tried with 4k,64k and 1MB block sizes time dd if=/dev/zero of=/mnt/testfile bs=1M count=10240 oflag=direct This gives me exactly results I expect: Using linear LVM, it's writing to one physical device at 187MB/s Using striped LVM with 4K blocks, it's writing to the striped LVM at 306MB/s, which is not quite double single drive speed but near enough for me to understand that "it's working". Using striped LVM with 64K blocks, it's writing to the striped LVM at 311MB/s Using striped LVM with 1M blocks, it's writing to the striped LVM at 312MB/s Plus all these results are sort of inline with the physical characteristics of the drives max R/W speeds. When I perform same procedure on a VM using the paravirtualised driver for the 3 controllers, I'm not getting speeds in-line with what I expect from solid state storage. Obviously, striped LVM in a VM with storage pool connected to the VM host just does not work the way it would with separate physical devices. /AH
