Wednesday, May 8, 2013

How much host writes does Windows 8 Fast Start feature use?

Windows 8 has a cool feature called Fast Start. When you enable it from Power Options dialog, it uses the hiberfile.sys to save part of the running state when you shutdown. So when you boot into Windows, it loads that part it saved to the hiberfile.sys directly to memory, instead of doing the full blown loading process. Like you expected, shutting down takes some time because it has to save whatever it needs to the disk before switching the power off.

At first, I thought this Fast Start feature saved only a small amount of information to the disk. But it turns out, it saves a considerable amount of information to the disk. I checked this by monitoring the amount of host writes to my SSD.

Previously I monitored the amount of host writes as at 27th of March to be 0.8GB. Then today (7th of May) I measured it to be 1TB. That’s roughly 200GB (it could be more or less depending on how Samsung Magician software rounds it off) in a span of 40 days. During that time, I only installed Octave and VMware Player to the SSD. It would have totaled to about 500MB. Maybe give another 10GB for temp files, browser cache, mail cache, Windows updates, driver updates and few other not-so-important things. Surely, it all wouldn’t take up 10GB. That’s all. The rest of it has to be those writes related to the Fast Start feature. So it’s roughly 5GB/day.


And I don’t even turn off my PC that often. On weekdays, I would do it twice. On weekends, only once. Restarts don’t count because then it does not save the state. So in total, it would come to about 70 shutdowns. OK, call it 100. Doesn’t matter how much it saves per shutdown. What matters is how much it saves per day. In total, that’s about 5GB per day. That’s a lot!!! That’s a lot of SSD wear and tear.

So, what I’m going to do is, I’m going to disable Fast Start and monitor for month and see how things progress. Since I haven’t done a properly controlled test, you can always argue these results are not valid. But it’s for your SSD’s own safety. Disable Fast Start if you value your SSD. Heck, you are only saving a couple of seconds of boot time. You can always use Standby. :)

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