Hello all,
Just recently purchased a Samsung 960 Evo NVMe drive. It is on a PCI
Express add-in card in a PCIe 2.0 x4 slot since the motherboard itself
does not have an M.2 slot.
On the main host machine, I ran "hdparm -Tt --direct /dev/nvme0n1" and
get the following:
Timing O_DIRECT cached reads: 2578 MB in 2.00 seconds = 1289.17 MB/sec
Timing O_DIRECT disk reads: 3962 MB in 3.00 seconds = 1320.20 MB/sec
The drive has one Ext4 partition on it. Mounted with "noatime" to the
/VMs mount point.
Host server is running Ubuntu server 16.04 and running "kvm --version"
shows QEMU emulator version 2.5.0.
When I run the same "hdparm -Tt --direct /dev/vda" on the hosts, it
shows quite a bit less:
Timing O_DIRECT cached reads: 1456 MB in 2.00 seconds = 727.51 MB/sec
Timing O_DIRECT disk reads: 2730 MB in 3.00 seconds = 909.76 MB/sec
Guest machines are setup with 10 GB of memory, 8 CPU (host CPU config
copied), virtio for disk bus, raw image file, with no cache. Guest
machines are also Ubuntu 16.04.
Before the upgrade, I was using an SSD in SATA III mode. The host and
guest disk reads were only a few MB/sec apart.
Is there something else I need to look at to see why the guests are only
getting about half the throughput of the drive?
Thank you!
Brian S.
