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Why does Hibernate have to be implemented?
Just as a matter of curiosity, Why does Hibernate have to be implemented
by checking a box in the Power options? Sleep is not like that. Off is not like that. Restart is not like that. Does this have something to do with public computers or shared computers, that managers wouldnt' want these hibernated but wouldn't mind sleeping them or turning them off? |
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#2
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Why does Hibernate have to be implemented?
micky wrote:
Just as a matter of curiosity, Why does Hibernate have to be implemented by checking a box in the Power options? Sleep is not like that. Off is not like that. Restart is not like that. Does this have something to do with public computers or shared computers, that managers wouldnt' want these hibernated but wouldn't mind sleeping them or turning them off? I don't really know. I can think of a few things, but I wasn't able to find a good conspiracy theory page with other good reasons. Most discussions of hibernation, seem to center around turning it on and off, without discussing why you might want to do that. 1) On a machine with 64GB system RAM, and an SSD drive to hold the OS, reserving a large hiberfil.sys is a waste of valuable storage space. People with hard drive storage for C: on the other hand, would not care. If I can afford to buy 64GB worth of DIMMs ($800 for good ones), I can afford a 4TB C: spinning hard drive :-) Usually, SSD boot drives are selected from the "small/cheap" category, and putting aside 48GB for hiberfil, isn't all that practical. 2) The hiberfil.sys is a snapshot of system memory. Only memory the OS "knows about", is recorded (not every byte need be captured, which is why the shutdown interval is relatively fast). There could be passwords stored in there. There exist options sometimes to erase files like that (like purging the pagefile at shutdown), but I don't think the hiberfil is necessarily covered. When Windows starts, it writes the "header" section of the hiberfil, but does not overwrite the body. Even after many reboots, information captured from days before, might still lurk in the later sections of the file. Only a hibernation option writes the body of the hiberfil, and if one section writes out a big image, a second hibernation writes only a small image, the tail end of the big image is still available for forensic analysis. The process that writes the hiberfil at shutdown, it uses lightweight compression. Which is why the hiberfil does not have to exactly match the size of system RAM. Note that this is problematic - if I put my mind to it, I could arrange a pattern stored in system RAM, which cannot be fitted into the hiberfile. The hiberfil compression scheme is making some assumptions about the typical contents of RAM, and not the worst case contents of RAM. So if a "villain" designs a test case for hibernation, it would be possible to break it. And have the hibernation attempt fail to find enough space. 3) Writing 48GB of compressed memory image to a rotating hard drive, would make the computer shutdown time take forever. Say the hard drive writes at 100MB/sec, 6GB per minute, worst case it would take 8 minutes to complete hibernation. (Worst case hardly ever happens in the real world.) At the next startup, you would wait another 8 minutes. So that's about all I've got in the way of ideas. I have hibernation enabled on this machine, as it isn't a "big" machine, and the issued involved aren't that significant. HTH, Paul |
#3
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Why does Hibernate have to be implemented?
micky wrote on 6/4/2015 7:16 AM:
Just as a matter of curiosity, Why does Hibernate have to be implemented by checking a box in the Power options? Sleep is not like that. Off is not like that. Restart is not like that. Does this have something to do with public computers or shared computers, that managers wouldnt' want these hibernated but wouldn't mind sleeping them or turning them off? Sleep IS optional - you can turn it off in the BIOS for example or by picking/defining a power profile that says "never". You can assign functions to the computer's restart/boot buttons also. Pulling the plug from the wall (or the UPS) is just about the only absolute action in this area. The reason that hibernation is treated special is that it can consume a lot of some resources (disk and some memory) while saving others (power). It's a tradeoff that makes sense in some situations but not in others so you are involved in the choice. Sleep is almost always a good idea for a home computer but almost never for a full-time server so different OS may have different defaults. Etc. -- Jeff Barnett |
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