Once upon a time, Marko Vojinovic vvmarko@gmail.com said:
On Tue, 23 Jun 2015 18:42:13 -0700 Gordon Messmer gordon.messmer@gmail.com wrote:
I wondered the same thing, especially in the context of someone who prefers virtual machines. LV-backed VMs have *dramatically* better disk performance than file-backed VMs.
Ok, you made me curious. Just how dramatic can it be? From where I'm sitting, a read/write to a disk takes the amount of time it takes, the hardware has a certain physical speed, regardless of the presence of LVM. What am I missing?
File-backed images have to go through the filesystem layer. They are not allocated contiguously, so what appear to be sequential reads inside the VM can be widely scattered across the underlying disk.
There are plenty of people that have documented the performance differences, just Google it.