NAS transfer speed: what limits a file copy?

A NAS transfer is only as fast as the slowest important part of the path. Upgrading Ethernet can help, but network speed is only one piece of the system.

Network link

At the theoretical maximum, 1 Gbps equals 125 MB/s, 2.5 Gbps equals 312.5 MB/s and 10 Gbps equals 1.25 GB/s. Real application throughput is lower.

Storage performance

Hard drives, SSDs, RAID layout, caching and simultaneous workloads can limit reads or writes. Small random files generally produce different results from large sequential transfers.

Protocol and CPU overhead

SMB or NFS processing, encryption, checksums and other work can consume CPU and add overhead. On older or entry-level NAS hardware this can become visible on faster links.

End-to-end matters

Check the client NIC, switch ports, NAS interfaces and negotiated link rates. For multi-gigabit transfers, the client storage also needs enough throughput to send or receive data at the expected rate.