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My HDD is slow 5400RPM and when working with 10GB size files it is impossible to use the computer until that big file finish re-creating a new copy/muxing/writing/etc. depends on process, the thing is it eats up all HDD speed and no other program can be used while this process runs.

So I was thinking maybe I could limit HDD write speed for programs I work with, so then it would reserve free HDD leftover speed to use for browsing internet or playing mp3s while the big files are being processed.

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I've never heard of a throttled HDD IO in Windows, at least natively. Have you tried setting the process priority?: wmic process where name="calc.exe" CALL setpriority "idle" – Marcelo Aug 11 '14 at 16:33
@Marcelo Priority dictates CPU time, not disk. When processing a large file, the disk is what is slowing the computer down, not the CPU. – Keltari Aug 11 '14 at 19:09
Related:… – Cees Timmerman Aug 11 '14 at 19:19
@Keltari Yes, I'm aware. I just thought that maybe modifying the priority for CPU could have some impact towards the final objective in the question. – Marcelo Aug 11 '14 at 19:27
If the computer is "unusable" when copying huge files, is it possible that you have forgotten to enable DMA? Normally, whether or not the disk is busy makes little or no difference since that happens without much (or any) CPU intervention. – Damon Aug 11 '14 at 19:45
up vote 14 down vote accepted

Unfortunately, you cant do that. Hardware is abstracted from applications and even parts of the OS. In essence, the application says "write this to disk" and the OS handles it. The application doesnt handle how or even when it gets written. All of this is handled at the driver and kernel level and there is no real way to change this.

Even if you could do this, the fact is you are using a spinning magnetic disk - and a very slow one at that - you wouldnt see much gain. The drive is constantly spinning and the heads are moving along the disk. Even if you wrote to your file less, the disk will constantly be seeking the right areas on the disk to read/write to/from.

Your best option would be to get another drive and do your work on that drive, leaving your first drive for your interenet, mp3s, etc.


You didnt mention how much RAM you have. Swapping could be a factor in the slow speed. Depending on how much RAM you have, adding more will only help.

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Wouldn't a Windows version of Linux' ionice come close to being an answer? – Daniel Beck Aug 11 '14 at 19:08
@DanielBeck There may be software out there that might work. However, who knows what complications might come from using it? It would be so much easier to just slap in another drive and be done with the issue. – Keltari Aug 11 '14 at 19:12
You can do it. See the dsulimano's answer to a similar question – niutech Aug 11 '14 at 21:47
I don't see any principled argument to why an application could not be throttled. Here's a very simple throttle: Suspend the process for 1sec every second. That throttles IO by about 50% and lets other processes slip in to use the disk. Seek times are on the order of 10ms. – usr Aug 12 '14 at 0:09
@usr: It depends on the type and frequency of I/O. Your approach works in some cases but not others -- e.g. if the I/O is happening entirely in kernel mode, I don't think you can always pause it by pausing the user-mode process. – Mehrdad Aug 12 '14 at 6:57

Process Lasso allows you to prioritize I/O. From their FAQ:

New in v4.1 (v4.09 beta), Process Lasso has explicit current and default I/O priority settings available those who require them. This only applies to NT6+ (Vista,Win7,...).

HOWEVER, Vista's I/O prioritization is based on the priority of the thread doing the I/O, which is dependent on the priority class of the process doing the I/O. There are actually only two levels of priority usable by applications, Normal and Very Low. Although there are technically 5, only these two are implemented or usable by processes.

Therefore, adjustment of the thread priorities will propagate to the I/O of that thread. In this way, Process Lasso already does I/O prioritization. Microsoft recommends applications adjust their I/O priority based by setting the calling thread's priority (directly or by adjustment of the process priority base class).

See also the paper on I/O prioritization from Microsoft.

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What I do when I have a process that keeps eating all my disk I/O on Windows is bringing up Process Explorer and pausing the offending process. After I'm done with my business and am ready to wait a bit I resume it. It's definitely not the most productive way of doing it since it's all-or-nothing way of controlling disk I/O and your process will have to wait while you use your computer, but so far I haven't seen any better alternative.

On the other hand, if you can do your process on Cygwin, you can install pv on your computer and use it as the first or final step with an option (I think it's -r) to throttle pv's output rate.

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