The Curious Case Of The Disappearing Disk Space

August 25, 2011 at 09:27 (Tech) ()

My laptop is a few years old now so I don’t expect it to run smoothly but it seemed to be getting worse. It finally clicked that part of the problem may be a nearly full hard drive, I’ve been moving around lots of video and it’s rare for my hard drive not to be practically full. So I started to tidy things up and clear some space, I removed games I was never going to play, uninstalled programs I didn’t use and cleared out quite a bit of space. The next day I didn’t have as much free space as I thought I’d cleared but I couldn’t be sure. I kept an eye on it and sure enough I was losing 5-10GB of disk space on a regular basis. I suspected some kind of virus but scans found nothing, could it be a problem with the disk? Too many defragmented files from moving huge videos around a lot? Disk cleaning tools cleared out space but not GBs of space.

I found out in Vista that 15% of the disk is allocated to shadow copies and restore points and there isn’t an easy way to change this. This had to be what was taking up the space, 15% would be 43GB which is quite a lot. So I restored to an earlier point before I noticed the problem and then cleared subsequent restored point. I started making backups and removed the large video files, finally I had 90GB free which I was happy with even if the shadow copy took another 40GB of it. I figured now would be a good time to run defragmenter on the disk and left it running overnight (and then some).

When the defragmentation was complete I had 5GB free. Something was still wrong. Time for more research. This forum post confirmed that it probably was a volume shadow copy problem. Reading this article at ZDnet made me aware but cautious of the vssadmin command and I found more details on vssadmin here.

Sure enough running vssadmin list shadowstorage showed the following:

Used Shadow Copy Storage space: 198.061 GB
Allocated Shadow Copy Storage space: 200.924 GB
Maximum Shadow Copy Storage space: UNBOUNDED

Allocated storage space 200GB! Maximum space Unbounded! It turns out that I wasn’t alone in having this problem. I can’t begin to imagine why anyone would desire no limit to be set, surely that just means all of your disk space would eventually be used. Turning System Restore Off and on again didn’t seem to recalculate the maximum space limit but at least cleared the other restore points. Funnily enough I don’t think I’ve ever used system restore apart from this week when I’ve been having this problem.

So I had to to set it manually:

vssadmin resize shadowstorage /for=c: /on=c: /maxsize=20GB

20GB is 7% but still seems generous. After a reboot I unsurprisingly had an extra 200GB free, hallelujah!

It seems to be okay now, I hope it stays that way, although I don’t quite know what to do with all that space now.



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