Re: [Libguestfs] [ovirt-users] Slow conversion from VMware in 4.1

On Tue, Feb 06, 2018 at 11:11:37AM +0100, Luca 'remix_tj' Lorenzetto wrote: > Il 6 feb 2018 10:52 AM, "Yaniv Kaul" <ykaul(a)redhat.com&gt; ha scritto: > > > I assume its network interfaces are also a bottleneck as well. Certainly if > they are 1g. > Y. > > > That's not the case, vcenter uses 10g and also all the involved hosts. > > We first supposed the culprit was network, but investigations has cleared > its position. Network usage is under 40% with 4 ongoing migrations. The problem is two-fold and is common to all vCenter transformations: (1) A single https connection is used and each block of data that is requested is processed serially. (2) vCenter has to forward each request to the ESXi hypervisor. (1) + (2) => most time is spent waiting on the lengthy round trips for each requested block of data. This is why overlapping multiple parallel conversions works and (although each conversion is just as slow) improves throughput, because you're filling in the long idle gaps by serving other conversions.