[PVE-User] Slow speeds when KVM guest is on NFS

Mikhail m at plus-plus.su
Wed Nov 16 11:02:26 CET 2016

On 11/16/2016 08:52 AM, Dietmar Maurer wrote:
>> 1) First guest inside qcow2 image, located on NFS share (via 10gbit
> What values do you get with raw images?

Just now converted guest's disk image to RAW, using default cache
settings. Seeing much better results - same "dd" test now shows 145 MB/s
write speeds:

541590+0 records out
35493642240 bytes (35 GB) copied, 245.511 s, 145 MB/s

(dd if=/dev/zero of=test bs=64k count=550k conv=fdatasync)

And I also tried same test over 1 gbit network, it shows acceptable
results there as well:

dd if=/dev/zero of=test bs=64k count=150k conv=fdatasync
153600+0 records in
153600+0 records out
10066329600 bytes (10 GB) copied, 94.1721 s, 107 MB/s

So something is not good with QCOW2 disk format.


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