Render time varies for no reason

[Mickmeister]

I've been doing some render tests, and I noticed that I can render the exact same scene multiple times, with no changes, and get different render times. Here are the render times I got from one test scene (minutes:seconds):

0:34
1:05
0:34
1:06
0:34
1:05
1:06
0:33

As you can see, the render times aren't completely random. It will render in either a short amount of time - varying only by a second or so (0:34, 0:33, etc) - or a longer one (1:05, 1:06, etc). The render is being done on 2 machines - the local and a remote server; I checked and made sure the remote machine wasn't failing during the longer renders. I tried rendering with Task Mgr open to see if some process was running that was slowing things down, but I didn't see anything suspicious.

Any ideas what might be going on here?

I'm using VRay 2.40.04, and Max 2014.

[Mickmeister]

Okay, I think I've got this figured out...it's looking like the server wasn't working during the longer renders after all. I thought I had ruled that out, but I just did some more tests and watched the buckets carefully, and I noticed that the server will work on some renders, and not on others. So it's no mystery any more why some renders take longer than others. But it's weird that the server will work for one render and not the next...it goes on and off for no apparent reason.

[Deflaminis]

There's a bit of a delay between frames after a server finishes a frame, and your render times are so short you might be hitting it during that window. I think with a 20 minute render you'll notice this less.

[Mickmeister]

Good to know...thanks.