windows 8 - Why is my disk at 99% usage here?

I have a similar issue as this user. You can pretty much take his screen shot and apply it to my issue: Windows 8.1, 99% disk usage or in that vicinity for a longer period of time (minutes). Yet the individual disk usage stats don't add up to more than roughly 1MB/Sec. I have an SSD disk capable of much higher throughput.

The question I linked to doesn't provide much answer, but one comment hints to low free disk space. That is an issue with my disk. I have only ~1GB left of free space on my C drive. But my follow-up question is why would that matter? Windows does pre-allocate 6GB of virtual drive, doesn't it? At least that's how I interpret "currently allocated" in the Virtual Memory settings screen under System Properties → Performance options.

I've tried to use the process monitor tool to gain some information on what's using the disk, but the amount of data logged in just a couple of seconds is so vast that I don't know where to start. The only thing I see is that service.exe accesses the registry a lot... But I guess that's normal? If anyone care to take a look, the log dump is here (19MB)

To summarize:

1. Does the disk usage really go up when free space declines? If so, why?


2. Can anyone deduct from my Procmon log file what program or process causes 99% disk usage?

edit: To comment on the "malware"-answer in the other post: I'd like to know, not guess. I doubt it is malware in my case, but if it is, my logs should show that.

update: Similar case just happened. Any clues from these two ResMon screenshots?

"System" doesn't really tell me much.

Answer

I've just seen your problem has gone away but below should be helpful for next time.

I downloaded your Process Monitor log and did a count for the number of times each file was being accessed during that 6 second trace you captured. You should be able to see this yourself in Process Monitor by going to Tools -> Count Values Occurences -> Select Path from the Column drop-down and then click on the Count button. Click the Count button to sort the count numbers in ascending/descending order. Double-click on any of those file paths to focus on them.

The top 4 file paths accessed are:
3276 times: HKCU\Software\Classes\Local Settings\MuiCache\de\417C44EB
3276 times: HKLM\SYSTEM\CurrentControlSet\Control\MUI\StringCacheSettings
2188 times: HKCU
1457 times: C: (this is the searchindexer that's accessing this)

Processes involved in the above accesses include SearchIndexer.exe and services.exe and they seems to repeating the request for accesses over and over again. Not I sure I know what's going on further than that but I suggest you try disabling your Windows Search indexer and see how that affects performance.

I also had another look at the trace in an unfiltered format and saw lots of access to various Software Distribution folders with paths prefixed with C:\Windows\SoftwareDistribution\Download..... so worth checking/disabling this and see how that affect performance.