11004 Views 6 Replies Latest reply: Apr 29, 2009 3:12 PM by cg0def
In theory, anything that you type including passwords and other personal information is temporarily saved into memory even though you don't administer any kind of save function. This temporary block of data could possibly get dumped into /var/vm and be recoverable. If you turn on Secure Virtual Memory these swap files are encrypted thus adds another level of security. Personally, I don't feel the need for this added security but in some situations, this might be advised.
I'm not quite sure about the performance hit when using Secure VM but I imagine the act of encrypting/unencrypting will slow down some activities like sleep, shut down and restarting. Its use would be effected by several variable and thus hard to test or benchmark.
In my opinion, it's an option to consider for secure networks and not really necessary for individual casual computing.
I'm also wondering the performance impact. I would like to add that each time your computer is 'swapping' (write down parts of RAM on disk to make space for recent applications) it will have to encrypt/decrypt the swapfile.
The process will be more frequent if you have less RAM or you open a lot of apps at the same time.
Actually your computer is using virtual memory regardless of how much ram you have in it. A lot of application simply cannot work properly without virtual memory.
Anyway I can't personally tell any difference between using secure vm and regular as far as performance goes. I have 4gb of ram on a 2.4ghz cpu an apparently that is fast enough. You should also make sure that the hibernation is set to the correct value for best performance.
Open terminal and type
pmset -g | grep hibernate
it should give you something like
Here's a list of what the numbers mean
0 - Legacy sleep mode. It will save everything to RAM upon sleeping but does not support “Safe Sleep”. Very fast sleep.
1 - Legacy “Safe Sleep”. This is the “Safe Sleep”. Everything your laptop goes into sleep, it will save everything to harddisk. Slow on Sleep and Startup.
3 - Default. As described above, when sleeping, contents are saved to RAM. When battery runs out, hibernate occurs.
5 - Behaves as 1 but applicable only for modern Mac that uses “Secure virtual memory”.
7 - Behaves as 3 but applicable only for modern Mac that uses “Secure virtual memory”.
if for some reason the variable is set to the wrong value ( 0 for example ) you could set it like this
sudo pmset -a hibernatemode 7
I should also point out that Secure virtual memory is a must in many government organizations and a lot of security minded admins require it as well. Dumping the virtual memory file and stealing important information from it is actually a very real danger and you should keep it enabled if you are dealing withe sensitive information like say bank accounts or other financial data. However, for most home users this is nothing to worry about.