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I have slow network transfer speed (26 MB/s). The beginning of the transfer started at 120 MB/s and dropped down every second.

I am transferring a 350 GB file from an E-Sata (7200rpm) drive mounted on Windows 7 to a Ubuntu Samba share (on esxi). The samba share is mapped to a drive letter on Win 7 by IP address.

ethtool eth0 shows:

Settings for eth0:
Supported ports: TP
Supported link modes: 10/100 half/full, 1000/full
Supports auto-negotiation: Yes
Advertised pause frame use: No
Advertised auto-negotiation: Yes
Speed: 1000MB/s
Duplex: Full
Port: Twisted Pair
PHYAD: 0
Transceiver: internal
Auto-negotiation: on
MDI-X: Unknown
Supports Wake-on: d
Wake-on: d
Current Message level: 7
link detected: yes

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Just try to test disk for wtite speed with dd in linux. and then check your network with iperf. and you ll know where is a bottle neck.

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The hard drive almost certainly only supports ~26MBps. Even the latest round of SATA drives can barely pull double that number (under idea conditions too).

That beginning speed of 120MBps isn't even really possible; 1000Mb / 8 * 80% = ~100MBps (realistic max). Windows caching is playing with the number, hence the high initial speed and after a while the number settles to the sustainable throughput.

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