Altering pmset for SSD?

benwiggy · 03-02-2013, 07:33 AM

I've read a lot of pages about changing the various config settings of pmset in the Terminal, after installing an SSD in a Mac laptop.

It makes sense to turn of Sudden Motion Sensing, as SSDs aren't really susceptible to the same kinds of motion that mechanical drives are.

But everyone says to change the hibernation mode, so that OS X doesn't write a sleep image to disk. This is to reduce wear on the precious SSD which may have limited writes.** Also small SSDs may find large RAM images take up too much room.

The disadvantage to this, as I understand it is that if you are caught short without power, and you need to keep using your laptop until it dies -- then you have to reboot, rather than continue from where you left off. I think I'm right that Apple's Resume mitigates some of the damage, but I suspect you might lose some data if you haven't saved.

Anyone have any factual info on this? Is it really such a burden? Any other settings to maximise battery life?

I've got a 247 Gb OCZ Vertex Plus, with 135 Gb free on a 2009 MacBook running 10.8.2, 6Gb RAM. I'm supposing that I'll get a new Mac within two years and normal wear on an SSD will not be an issue in that time.

** For some reason, I'm reminded of the bit in Fawlty Towers, where the fierce old lady says she doesn't turn her hearing aid on because it wears out the batteries.

benwiggy · 03-04-2013, 01:33 PM

OK, I think I've finally cracked it.

The pmset man page goes on about Standby Mode, but this only applies to newer Mac laptops.
Supported hardware will thus hibernate if they have been sleeping for a while.

So, my 2009 MacBook was factory configured to sleep and not hibernate, and to power the contents of memory until the battery became very low: only then it would hibernate.
That explains the loss of 1-2% overnight -- or considerably more if you left it sleeping for a few days.

I thought that because my MB didn't support "standby", it could use use hibernationmode 25. But this is not the case. By changing the hibernationmode to 25, the MacBook will hibernate, rather than sleep, saving the contents of memory to disk and powering down the RAM. Opening the lid or pressing a key isn't enough to wake: you have to press the Power button. After some progress "slits", memory is restored. This is not a reboot: it's a wake from hibernation. So unsaved documents should still be there.
A key difference between hibernation and sleep is that in sleep, the little light will pulse; in hibernation, it's off.

So: this seems to be the best of both worlds: lower writes to the SSD; better battery life while not used. The only down side is the slightly longer wake time. (I wish I'd known this in 2009!)

03-02-2013, 07:33 AM	#1
benwiggy League Commissioner Join Date: Aug 2006 Posts: 5,040	Altering pmset for SSD? I've read a lot of pages about changing the various config settings of pmset in the Terminal, after installing an SSD in a Mac laptop. It makes sense to turn of Sudden Motion Sensing, as SSDs aren't really susceptible to the same kinds of motion that mechanical drives are. But everyone says to change the hibernation mode, so that OS X doesn't write a sleep image to disk. This is to reduce wear on the precious SSD which may have limited writes. Also small SSDs may find large RAM images take up too much room. The disadvantage to this, as I understand it is that if you are caught short without power, and you need to keep using your laptop until it dies -- then you have to reboot, rather than continue from where you left off. I think I'm right that Apple's Resume mitigates some of the damage, but I suspect you might lose some data if you haven't saved. Anyone have any factual info on this? Is it really such a burden? Any other settings to maximise battery life? I've got a 247 Gb OCZ Vertex Plus, with 135 Gb free on a 2009 MacBook running 10.8.2, 6Gb RAM. I'm supposing that I'll get a new Mac within two years and normal wear on an SSD will not be an issue in that time. For some reason, I'm reminded of the bit in Fawlty Towers, where the fierce old lady says she doesn't turn her hearing aid on because it wears out the batteries. Last edited by benwiggy; 03-02-2013 at 07:36 AM.

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03-04-2013, 01:33 PM	#2
benwiggy League Commissioner Join Date: Aug 2006 Posts: 5,040	OK, I think I've finally cracked it. The pmset man page goes on about Standby Mode, but this only applies to newer Mac laptops. Supported hardware will thus hibernate if they have been sleeping for a while. So, my 2009 MacBook was factory configured to sleep and not hibernate, and to power the contents of memory until the battery became very low: only then it would hibernate. That explains the loss of 1-2% overnight -- or considerably more if you left it sleeping for a few days. I thought that because my MB didn't support "standby", it could use use hibernationmode 25. But this is not the case. By changing the hibernationmode to 25, the MacBook will hibernate, rather than sleep, saving the contents of memory to disk and powering down the RAM. Opening the lid or pressing a key isn't enough to wake: you have to press the Power button. After some progress "slits", memory is restored. This is not a reboot: it's a wake from hibernation. So unsaved documents should still be there. A key difference between hibernation and sleep is that in sleep, the little light will pulse; in hibernation, it's off. So: this seems to be the best of both worlds: lower writes to the SSD; better battery life while not used. The only down side is the slightly longer wake time. (I wish I'd known this in 2009!)