TRIM Support in Mac SSD

Question

I am about to purchase my first Mac and Im so excited. But before I do I have a question about the SSD. I was not planning on buying the SSD, but instead just going to some 7200RPM HDD but realized the price was only an additional $90, a price you can not just go out and buy one at.
My only concern is the lack of TRIM in Mac OSX. Now, their is speculation (and partial proof) that Lion will have TRIM support, but from what I have researched TRIM is also a hardware variable and not just software. Does anyone know if the new MacBook Pro's SSDs offer TRIM support? Also, will my SSD, by Summer hopefully, be negatively effected by the few months of the lack of TRIM?
Thank you so much,
Ben

Answer 1

You do not need to run any UNIX (or any other) programs to 'TRIM' the drive. If the drive firmware supports TRIM (as all newer drives do) and the operating system supports the TRIM command, you will benefit from this feature. The way TRIM works is this:
When you delete a file from a drive, the operating system marks the space used by the file as free so it can be used again. On a mechanical hard drive this works fine and the space will get written over as needed. Unfortunately, the SSD does not know the difference between erasing a block and writing over it with new data, so they are treated the same. The problem that occurs with SSD is that each block on the drive has a limited number of write cycles it can withstand before failing so the SSD firmware tries to spread out the usage of blocks on the drive by a process called wear-levelling. This ensures that the drives last as long as they need to, but results in fragmentation of the drive. This is a lower level fragmentation than what is typically referred to when discussing hard drive fragmentation and is not really related. This low level fragmentation can result in reduced performance of the drive over time, as blocks are erased and data is moved around by the wear-levelling.
The drive manufacturers have worked wonders trying to minimize this effect with intelligent firmware, but it is still a measurable problem. This is where TRIM comes into play. If the TRIM command (a low level drive command, not something you run from within the operating system) is supported throughout the system, deleting of a file will cause the operating system to issue TRIM to the SSD instead of just marking the blocks as empty as would be done on a mechanical hard disk. The SSD then knows that these blocks are no longer needed and the drive firmware can then clean up more efficiently. The drive firmware will show the space as available (because it is) but will not actually perform a write to that part of the drive until a later time, when enough blocks are ready to be TRIM'd all at once. This works in conjunction with the wear leveling to reduce wear on the flash cells and prevent fragmentation from occurring. For a more detailed description of TRIM, I recommend checking out the articles by Allyn Malventano over at PC Perspective:
http://www.pcper.com/comments.php?nid=7488
That site is mostly geared towards Windows users, but the basics of SSD operation are the same, and Allyn is definitely an expert when it comes to storage technology.
As far as over-provisioning goes, this provides a way to reduce fragmentation without the need for TRIM support (although the SandForce drives also can do TRIM). Over-provisioning involves setting aside a certain amount of flash memory on the SSD (7-28% typically) that is not available (or visible) to the operating system. The firmware uses this extra storage space to more efficiently defragment and wear-level the drive and it is transparent to the operating system. This is why an Intel X25 G2 drive will benefit more from TRIM support than a SandForce based drive like the OWC or Vertex series ones. The above mentioned site also has some good articles about over-provisioning, including comparisons of the same drive with 7% and 28% overhead. It boils down to this: if you have a SandForce drive, TRIM support is not as important because the drive does a good job on its own. If you use a different SSD, TRIM support is very beneficial, and we should all hope that OS X delivers full support for TRIM in the near future. Also, the added expense for the enterprise level (28% over-provisioned) SandForce drives is normally not justified, especially in a single drive setup.