[CentOS] qeum on centos 8 with nvme disk

Sun Oct 13 19:43:24 UTC 2019
Stephen John Smoogen <smooge at gmail.com>

On Sat, 12 Oct 2019 at 17:38, Jerry Geis <jerry.geis at gmail.com> wrote:
> Hi All -  I use qemu on my centOS 7.7 box that has software raid of 2- SSD
> disks.
> I installed an nVME drive in the computer also. I tried to insall CentOS8
> on it
> (the physical /dev/nvme0n1  with the -hda /dev/nvme0n1 as the disk.
> The process started installing but is really "slow" - I was expecting with
> the nvme device it would be much quicker.
> Is there something I am missing how to get a faster disk access ?

Does anything get listed in the guest or the virtual-machine-host
system for errors? The reasons I could see for very very slow nvme
would be that something is trying to write too small a sector for the
drive and flushing the drive. Depending on the nvme it might be set up
to read mostly and write rarely, read/write even or write a lot/read
in blocks. VM's usually are mixed use and get really weird behavior on
the others. If the nvme is expecting large writes and it is getting
small ones which don't "fit" it will 1) wear out the nvme because it
is basically rewriting a full block every time even if it is only
changing 5 k and 2) is slow because all those little writes are

I would look to see if the device is mostly in Device Wait and if io
errors are showing up.

Stephen J Smoogen.