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Old Feb 26, 2009, 01:01 PM   #1
louden
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SSD Tweaks in Mac OS

Does anyone have any knowledge of SSD tweaks for Mac OS to either:

a) extend the life of an SSD drive
b) make the environment faster?

I've seen more than a few tweaks for Windows - more because they're needed, but still think there's room for improvement in Mac OS.

I'd be happy to maintain a list of tweaks based on replies to this thread:

MAC OS Changes:

App Changes:
Firefox:

Move your cache to RAM: (From http://mydellmini.com/forum/windows-...aks-t2540.html):
Description: If you use Firefox, there's a way to write cached files to RAM instead of the hard disk. This is not only faster, but will significantly reduce writes to the SSD while using the browser.
Instructions: Open Firefox -> Type about:config into the address bar -> Enter -> double-click browser.cache.disk.enable to set the value to False -> Right-Click anywhere -> New -> Integer -> Preference Name "disk.cache.memory.capacity" -> value memory size in KB. Enter 32768 for 32MB, 65536 for 64MB, 131072 for 128MB, etc. -> restart Firefox
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Old May 24, 2009, 12:54 PM   #2
jazz1
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Quote:
Originally Posted by louden View Post
Does anyone have any knowledge of SSD tweaks for Mac OS to either:

a) extend the life of an SSD drive
b) make the environment faster?

I've seen more than a few tweaks for Windows - more because they're needed, but still think there's room for improvement in Mac OS.

I'd be happy to maintain a list of tweaks based on replies to this thread:

MAC OS Changes:

App Changes:
Firefox:

Move your cache to RAM: (From http://mydellmini.com/forum/windows-...aks-t2540.html):
Description: If you use Firefox, there's a way to write cached files to RAM instead of the hard disk. This is not only faster, but will significantly reduce writes to the SSD while using the browser.
Instructions: Open Firefox -> Type about:config into the address bar -> Enter -> double-click browser.cache.disk.enable to set the value to False -> Right-Click anywhere -> New -> Integer -> Preference Name "disk.cache.memory.capacity" -> value memory size in KB. Enter 32768 for 32MB, 65536 for 64MB, 131072 for 128MB, etc. -> restart Firefox
Is there any similar tweak for Safari Beta4?
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Old May 26, 2009, 10:48 AM   #3
wankey
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Seconded. I'd rather Safari use up my massive amuont of ram than try to write to disk all the time. I happens a lot when I view large images.
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Old May 27, 2009, 02:31 AM   #4
VirtualRain
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You guys may want to read through this thread on the OCZ forums for the Vertex SSD's... http://www.ocztechnologyforum.com/fo...ad.php?t=52845

Note that this guy who previously worked at Apple had the following to say about RAM Disks...

Quote:
That thing is snake oil, as are the vast majority of ramdisk products on OS X. Designing a ramdisk that works well on OS X is remarkably difficult because backing a block device into wired memory causes the contents to be double buffered above it in the Unified Buffer Cache.

For transient data on systems with no VM pressure, what will happen is the file is created, the object backing it sits in the UBC, it might get synched to disk, but unless you are running low on ram it stays in ram as well. That is why you see no speed increases, all you are doing is eliminating the background asynch writeout, and you are wasting a lot of ram to do it. More importantly, if you are actually creating a wired ram disk you are eating a ton of kernel address space which can be an issue if you have a lot of memory (large page tables) or several video cards.
Additional comments...

Quote:
Okay, so just to prove I am not just a grumpy old naysayer, here are some things you could do to actually improve performance under OS X.

1) Disable Adaptive Hot File Clustering

This is a feature of the OS that tracks how often files are used and automatically moves them closer to the outer rim of the drive (which is faster on conventional disks). On an SSD it is just a useless block move.

2) Disable automatic defrag

This actually might not be a win, because the system only performs auto defrag in very limited cases (files less than >20 megs with more than 8 extents), and while defragging the file itself will not be a performance win, consolidating its metadata into the file record (so you don't have to walk through the extents btree) might in fact be a win even on an SSD because it significantly reduces the amount of reads you have to do figure out where the file is.

The unfortunate thing is that there is no simple way to do either of these. You could build a custom kernel (it is a ~1-2 line change to short circuit them out). I suspect that neither is going to be a particularly large win though, so you are better off just running a stock (supported) kernel.
It seems there's really little that needs to be done or can be done.
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