[ovirt-users] Strange drive performance over 10Gb

[Yaniv Kaul]

On Dec 1, 2017 5:50 PM, "Wesley Stewart" <wstewart3 at gmail.com> wrote:

I have been fiddling with the drive settings in the windows guest and have
been able to fix a lot of the issue.  I went into Device manager -> Disk
Drives -> (right click) QEMU QEMU HARDDISK -> Policies and checked "*Turn
off Windows Write-Cache buffer flushing on the device*"

I am not sure how safe this is to do in a virtual machine, but my 10Gb
transfer speed is now much more stable.  Occasionally it dips to the low
100 MB/s or so, but generally stays at 200-300 MB/s.


It's safe until you have an unplanned power failure, and then some
undetermined amount of data might be lost.
Y.


On Thu, Nov 30, 2017 at 10:39 PM, Wesley Stewart <wstewart3 at gmail.com>
wrote:

> I was curious if anyone else has seen this or had any suggestions.
>
> I have recently began playing around with my two servers (Freenas Box and
> oVirt box) and their 10Gb Ethernet ports.
>
> I can access the Freenas SMB share over the 10Gb port without issue and I
> have been playing around with the capabilities.  After finding out that my
> Linux Raid (MDADM) mirror is having horrible write performance, I decided
> to plug in an NVMe drive that I had lying around and check out its
> performance.
>
> *For my first test*,I added the NVMe drive as a passthrough device to a
> Windows guest and was able to transfer to and from Freenas box without
> issue.  Speeds were typically ~350-400 MB/s but could drop down to 250 MB/s
> or so, and would top out around 525 MB/s, pretty slick!
>
> *For my second test*, I decided to mount the NVMe drive on the CentOS
> ovirt host and make it a local datastore.  I migrated my Windows Guest to
> it, and decided to test and see what sort of transfer speeds I got and saw
> some weird results...
>
> Writing TOO the NAS worked about the same.  Perhaps a little slower but at
> least had a steady 250-300 MB/s.
>
> Writing to the Windows Guest had a very "Fast and then slow, fast and then
> slow" type of throughput.  I took a few screenshots:
>
> (Writing TO the NAS was fairly consistent)
>
> [image: Inline image 1]
> https://i.imgur.com/jWNNvfp.png
>
>
> (Writing TO the Windows Guest on NVMe storage)
> Sometimes these hit the *low 10-20 MB/s* during the transfer.
> [image: Inline image 2]
> https://i.imgur.com/aizG6n0.png
>
> [image: Inline image 3]
> https://i.imgur.com/AjRpR0K.png
>
>
>
>
>
>
>

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