XCPNG VM NFS Disk Speeds Faster than Ethernet Link!

Computer Hardware & Server Infrastructure Builds
1

Hi,

I’ve been testing XCPNG with TrueNAS as a storage location for VM disks, and I have copied over an existing Windows VM for local SSD storage to the remote TrueNAS NFS share. The link speed is only 1 Gbps (so roughly 125MB/s max), yet somehow, Crystal DiskMark and Task Manager show read speeds at over 1GB/s (1000 MB/s). When I look at the network graph on the TrueNAS dashboard, it does peak at 1 Gbps. Is there some sort of caching that XCPNG does? I can’t figure out how it’s possible, and it does appear to actually be on the NFS share rather than local. When I turn on sync in TrueNAS, the write speed is down to 34 MB/s, and at one point, the read was as well. But on subsequent runs with sync on, read went back up to 1GB\s with write staying quite low.

Regards,
Abdullah

2

I think there is some caching from XCP-ng and most likely there is more caching in the guest OS as well.