Often, especially when I'm running a long-running process that uses a lot of RAM, the process will get half way through then crash because Windows thinks there's no more available disk space. Then I restart the PC to discover everything is fine, there's still more than enough space for the process to finish. Why?

Does Microsoft assume that "everyone has a 500 GB or larger hard drive these days, so we can waste as much of their space as we like"? Well I have a 6 year old MacBook Air with a 128 GB SSD, and even the newer ones only come with 256 GB.

For example: I just tried to use Deluge to download a 16 GB torrent file on to my D: drive (system partition is C: as it is on 99% of PCs) while File Explorer was showing 18 GB of free space on that drive. Giving me a theoretical wiggle room of 2 GB, right?

No other programs running at the same time, no Windows Updates dl'ing in the background (as far as I can tell), no other obvious reasons for 2 GB to be inadequate margin. Yet the download stopped at 68%. I had to restart, force re-check in Deluge and continue before it happened again at 84%!

Another restart resulted in the dl finally completing and being left with the expected 2 GB of space on D:. So why is this happening?!?! Am I missing something really obvious here because I still don't get it...and it doesn't just happen with Deluge, it happens with all sorts of programs.

Oh and BTW, don't know if this is relevant but I've never seen my system RAM usage go above 80%...not even once. I only have 4 GB but that seems to be more than enough for what I do regularly.

  • We don't have nearly enough information to help you. What's that long-running process, is it something specific or anything that runs long enough? How does it crash? Why do you have to reboot? How much used space does Explorer show before crash, after crush but before reboot and after reboot? Do you by any chance have pagefile configured on that drive? – gronostaj Jan 21 at 13:23
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    Please elaborate your question. The reasons why you could be out of space are numerous. For example, lack of free RAM will cause Windows to use swap which could become pretty huge. – montonero Jan 21 at 13:23
  • Sorry guys thought I was being detailed enough but obviously not! Anything that runs long enough will cause the problem, and "long enough" is usually ~30 mins or longer. It doesn't crash per se, but complains about no disk space in whatever fashion that program was designed to. I have to reboot to get Windows/the program to realise that there is still plenty of space available. Enough space for whatever I'm doing + extra before I start the process, 0 bytes remaining after but before reboot, many GB after reboot. I thought it might be the pagefile, but apparently there is none on D: :( – Kenny83 Jan 21 at 13:46
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    When you reboot the OS will run disk integrity checks which may roll back filesystem transactions that are allocating space. It is entirely possible the immediately prior to your crash there was no space left. Programs can allocate or lock disk space as they need it and a reboot will release it. We don't know what programs you are running or what you are doing so it is difficult to offer any help. It could be Windows Update temporarily allocating space, you downloading things or thousands of other programs. – Mokubai Jan 21 at 14:22
  • @Mokubai Hmm interesting...thanks! I thought that this might be a performance feature of Win 10, like maybe it uses your SSD for swap space just to speed things up. But that wouldnt make sense anyway, since RAM is 100x faster than a storage device ever could be (although modern SSDs are starting to catch up from what I've read). Meh, I guess I'll just have to deal with it for now. But I'm still confused as to how I could e.g. have 18 GB free before starting a 16 GB dl, then the dl crashes half way through. Surely 2 GB is enough for whatever Windows is doing in the bg (no other progs running)?! – Kenny83 Jan 21 at 14:45

There are several reasons this happens, but the most critical piece you're missing is how downloads work. When you are conventionally downloading a 16GB file, you may actually need 32GB free, because the file is downloaded as a "partial" download until it's complete, then it actually writes the completed download as a new file which is saved. There are different download mechanisms, but if you watch the download progress in the folder where you're saving a conventional download, you can often see the partial download as it is marked in some way (e.g. "filename.partial").

When you are downloading Torrents, you have the additional factor that the pieces may come from different sources, and therefore be different sizes, each time you attempt the download. So a Torrent download is more like "assembling" a file from pieces, than like a traditional download of an intact file.

The best explanation of this process that I could locate is at How Torrent Downloading works .

In addition, there are other ways that your system temporarily consumes disk space until you restart. Most visible are just temp files that are open while given applications are open, essentially the "working files", which are often removed on closing the app. On a Mac, there is also swap file space; there is a discussion at Question about Mac restart freeing up disk space about this phenomenon, although not all the comments are technically correct.

  • OK so with Deluge set to use "Full Allocation", it doesn't allocate all space necessary and download straight into that space? This is how I'd do it if I wrote a torrent app :S – Kenny83 Jan 23 at 0:03

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