Vista Tips - Remote Differential Compression

I've read a few Vista tips claiming that disabling Vista's Remote Differential Compression improves copy times, even with local transfers. To tell you the truth I don't copy that many files between computers mainly because I have a fairly "slow" 802.11g wireless network (~ 1 MB/sec speeds) and if I have to transfer a large amount of data I just use a USB stick. Anyways, back to Vista's RDC, I thought I might give it a try locally and compare it to XP - as everyone else I feel that Vista's copy times are not as good as XPs.

Tests were conducted on the only machine I have both Vista and XP, the tiny ASUS R2H, standard configuration + 1.2 GB RAM. Both Vista and XP were up to date, Vista SP1 and XP SP3, no antivirus. The tests are performed using the standard copy functionality, in both systems I waited for the copy window to go away (copying in Vista goes quite slow at the end and the window hangs on for a second or two).

The initial test was using a 1 GB test file created with fsutil file createnew and was basically consisting of the usual copy operation of the test file between two folders on the same partition. Each test was performed 3 times to get an better view, when the OS was idle, before each run I called ProcessIdleTasks, wait for idle and then run Sync (I don't know any other utility to flush the data from the buffers). Here are the results:

	Test #1	Test #2	Test #3
Windows XP	1:20.320	1:21.000	1:20.390
Windows Vista without RDC	1:13.050	1:24.830	1:27.290
Windows Vista with RDC	1:29.300	1:12.670	1:12.360

To be honest, the results are a bit mixed, the copy in Vista "felt" slower but it wasn't really that much behind XP. The overall timings didn't look right and then I thought it may be due to the fact the test file was basically a "space" filled file, so I though I might give it another try, this time with a test file generated with random content using MyNikko's Dummy File Creator. Here are the new results:

	Test #1	Test #2	Test #3
Windows XP	3:04.450	2:36.570	2:37.030
Windows Vista without RDC	2:28.780	2:22.700	2:35.490
Windows Vista with RDC	2:22.440	2:37.500	2:40.080

The timings don't seem to be consistent and I believe that is due to the different file allocation every time - the machine wasn't doing much else, explorer.exe was the only one in top using not too much CPU. The Vista with RDC disabled seems to be slightly faster, to my surprise it looks even faster than XP, although overall copying in Vista "felt" slower than XP - maybe XP feels faster than Vista just because Vista has a finer progress bar and you can actually notice when the copying is faster at start-up and then it gradually gets slower for some reason, then at the end it gets really slow and the copying window just stays on for a second or two. But from what I can see in my case, Vista with RDC off is about as fast as XP if not faster when copying the 1 GB test file.

Well, as a conclusion, this may not be the best test scenario as RDC is supposed to affect transfer over the network, the "tip" seems to confirm somewhat, even with local transfers - I may have another go accross local network sometime next week. Personally, I will keep RDC disabled just because it felt a bit quicker and I don't have another RDC capable machine on the network to take advantage of the feature. I can see though the potential advantage when transfering large files that change very little between two RDC capable machines (e.g. Outlook .pst files between say Vista and Windows Home Server?!) but I don't think this is much help for the usual home user. Definitely recommend trying it for yourself and see which one's better for you, on or off - see the steps here (screenshots) on how to enable/disable Remote Differential Compression.