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When I built my new computer, I gave my old one to my parents who were in dire need of an upgrade, after cleaning everything out of it, of course, leaving just the OS and a few programs. It worked fine for a while, before it started to fail to load Windows (it would just get stuck). After investigating this behavior and asking around, I decided that it might be a failing hard drive, so I pulled it out and plugged it into my own computer to run chkdsk on it (I initially did this to try and boot to the drive, but since my computer is set up with RAID and that Windows installation didn't have RAID drivers, I just booted into my own Windows 7 installation and ran chkdsk on it).

I did this last Friday evening, and it's been running since then (which makes it about 6 days so far). I am not surprised since it can be slow, it's a 1 TB hard drive, and a Western Digital "green" one at that, so it's likely running at a slower RPM anyway. I do see it make progress, so I know it's not stuck, and the hard drive light has been perpetually on, on my computer, which I haven't used for much of anything else, other than sharing files over the network and light web browsing, while this has been running.

My computer has 16 GB of RAM, and is running Windows 7 Pro x64. Why does chkdsk take up 90% of that? It's holding that level steady, and has been for days, going between 90% and 91%, as it frees and fills memory constantly. CPU usage is very low (which I expect since this is a very I/O heavy operation).

It doesn't look like anything bad is going on, but I am curious. Why is chkdsk taking up so much memory? I am at least glad that it seems to be doing this intelligently, as it's maintaining a high level without starting to thrash the main HDD by paging.

Does anyone know? Is this normal?

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If it's been running for several days, I'm assuming that you ran chkdsk with the /r flag.

With Windows 7, using that much RAM is normal. Source

The file system team immediately began to look into the issue. [...][F]rom their perspective the memory usage was by design and was a specific Windows 7 change for this scenario (the /r flag grabs an exclusive lock and repairs a disk and so our assumption is you'd really like the disk to be fixed before you do more stuff on the machine[...]).

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I am using the GUI, but I did check the checkbox to scan for and attempt repair of bad sectors, which is the equivalent. Thanks for the link! –  Ben Richards Aug 26 '11 at 1:42
    
It's not just Windows 7; Windows 2008 R2 gets into this unimaginable state as well. I bring down a single disk for checking, and chkdsk absolutely needed to consume 20GB of RAM for that single disk and slowing the rest of the server down. That is not a mistake, 20GB of memory. –  icelava Mar 9 '12 at 8:02
    
@icelava: Considering that 2008 R2 is a continuation of the Windows 7 code base, that's not surprising. This will probably affect all newer OSes as well. –  afrazier Mar 9 '12 at 14:52
    
I checked my external 2TB NTFS disk without the /r (or any other) switches and it still consumed almost all RAM (I have 5 GB). Windows 7 64bit. –  David Balažic Aug 30 '12 at 11:19
    
Interesting. I just ran it against a 1.5 TB disk and it didn't even make it to 1 GB on an 8 GB system. I'd expect a read-only check to only use as much RAM as required. –  afrazier Aug 30 '12 at 13:27
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I am running CHKDSK /r on a Seagate 1TB SATA 3GBs drive at the moment - Windows 7 x64 Ultimate, CHKDSK is consuming 31GB of my 32GB RAM. However, if you load up another program such as After Effects, CHKDSK releases RAM to allow the program to run quite well.

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