Benchmarking Windows 7 Offline Files Transparent Caching
Windows 7 comes with several features that promise to greatly improve file access over a WAN. One of them is version 2 of the SMB protocol, another transparent caching. This article describes how I measured their effectiveness.
SMB2
SMB2 is said to be much less “chatty” and thus more efficient on WAN links. To verify this, I copied 3 different sets of files over a simulated WAN link (bandwidth 2 MBit/s, latency 25 ms). I performed the test both with Windows XP and with Windows 7. Copy source was a NetApp system that supports SMB version 1 and 2.
| Test | Windows XP | Windows 7 | Speed increase |
| Large files 16 files, total size 316 MB, avg. size 20 MB |
1,500 s | 1,438 s | 4% |
| Small files 370 files, total size 14,8 MB, avg. size 41 KB |
171 s | 124 s | 27% |
| Very small files 199 files, total size 174 KB, avg. size 895 Bytes |
55 s | 34 s | 38% |
Transparent Caching
This nifty feature stores files that have been copied once to the local machine in the offline files cache. If the file is accessed again, it is fetched from the offline files cache instead of going to the file server a second time. I tested the potential performance benefits of transparent caching by repeating the SMB test above (after rebooting both computers to empty their file system caches).
Transparent caching needs to be enabled via the group policy setting Enable transparent caching in Computer Configuration\Administrative Templates\Network\Offline Files. Enable the setting and set a minimum latency for it to operate – only if the file server is further away will its files be cached. I used a value of 10 ms in this test which is well below the 25 ms latency of the WAN link.
| Test | Windows XP | Windows 7 | Speed increase |
| Large files 16 files, total size 316 MB, avg. size 20 MB |
1,496 s | 10 s | 99% |
| Small files 370 files, total size 14,8 MB, avg. size 41 KB |
163 s | 51 s | 69% |
| Very small files 199 files, total size 174 KB, avg. size 895 Bytes |
54 s | 27 s | 50% |
Conclusion
As you can see, both technologies improve file access over WAN links compared to Windows XP’s SMB1. Combined they make Windows XP look very old. If you have not done so yet, give transparent caching a try.
