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OSX and SSD drives

Last response: in Storage
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September 4, 2012 7:23:28 PM

I know that defragging an SSD is bad for it, just wears it down and not needed. However, after reading this about OSX I wonder if the HFS+ filesystem in OSX wears SSD drives faster?

Quote:
Fortunately, Mac OS X's HFS+ filesystem has some safeguards against avoidable fragmentation. First, the filesystem avoids using space recently freed by recently deleted files whenever possible, looking instead to potentially larger, already free portions of the disk first. Second, Mac OS X 10.2 has a routine that clumps smaller portions of disk space into larger portions on the fly. Finally, Mac OS X 10.3.x can automatically defragment some files through a process called "Hot-File-Adaptive-Clustering." Though these routines have undoubtedly have made consequential fragmentation a less common occurence, their efficacy is not beyond question. First of all, though they can reduce fragmentation of extant files, they can also cause remaining free portions on the disk to become smaller in size, potentially leading to more fragmentation down the road as new files are written. Second, the automatic defragmentation routines will not work on certain files -- specifically those above 20 MB nor those fragmented into 8 or fewer segments.

Source

So HFS+ controls what areas of the drive are written to which in the case of SSD you would not want this. You would want even wear across all cells.

Anyone more knowledgeable than myself want to sound off?

More about : osx ssd drives

a b G Storage
September 4, 2012 9:35:31 PM

If you look at what you quoted, it's talking about 10.2 and 10.3, and they're up to 10.8 now. Given Apple is now shipping it's own semi-proprietary SSDs in virtually every unit, meaning they are on the hook for replacing them under warranty if they go bad... I would expect that they have been quietly improving support for this on the back end in advance of shipping the first Air model with the SSD.
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September 4, 2012 9:48:05 PM

I suspect you are right, it is apple after all who are fastidious if nothing else. I was just wondering if anyone had an indepth knowledge of how the current OSX works.
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September 4, 2012 11:26:32 PM

The drive's controller/firmware uses wear leveling, TRIM, and other algorithms to determine which cells and blocks are used to store data. HFS+ (or any file system) does not have any idea about how the individual bits are mapped in flash storage.

As for as Apple increasing support for SSDs, they only activate TRIM support on drives they ship. Third-party SSDs will have TRIM disabled. That being said, I've used an Intel X25M SSD in my MacBook Pro since 2010 without any issues.
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September 12, 2012 2:56:47 AM

I'd think there is some way to hack trim into working. I have it working on mine but that's because it was an option for multibeast when installing ML on my hackintosh.
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