If you’ve researched using an SSD before, you may have heard how they can slow down over time. Most manufacturers go out of their way to avoid this by suggesting users run TRIM, a command for cleaning up “garbage” files. But what if you had an SSD so advanced, with a perfect combination of technologies designed to stay at peak performance and speed throughout its life that you had no need for TRIM? Well, you’d have an OWC Mercury SSD, of course!
First, we should note that support for TRIM is based on the operating system and the SSD manufacturer. Microsoft Windows began to natively support the TRIM command for SSDs in Windows 7. Apple added TRIM support in 10.6.8, however Apple does not natively support TRIM on non-Apple SSDs. There is a way to hack the Mac OS to support TRIM on non-Apple SSDs, and we will get into that later on. But before we go further into what TRIM is and why you do not need to be concerned about enabling it on your OWC SSD, let’s take a closer look at some SSD basics.
When data is written to a new SSD, that data is stored in small pieces called “pages”. These pages make up blocks, which make up the SSD. Let’s think of pages as a house, a block as a city block, and the SSD as the city. SSDs keep track of which pages have information saved on them, and this is called the Logical Block Address (LBA). Think of the LBA as a city registry that knows where everyone lives.
When data is written to the SSD, it is first written to the empty pages. In our analogy, a family would move into an empty house within the city block first. When data is deleted from an SSD, the information is not actually deleted. The reference of the data is removed from the LBA, but the data is not actually erased. This lingering unused data is called invalid data. It is like a family moving out of the house and having their name removed from the city registry, but leaving all of their belongings behind. Having this leftover information means no further information can be written to the block before it is completely erased.
Once the SSD starts running out of empty pages, it will begin looking for invalid pages that can be erased, but SSDs cannot erase just an individual page. It must erase the entire block so the task of relocating the valid pages of data is created. This movement of valid data to different blocks on the SSD is called write amplification. Moving valid data to another block and then erasing the invalid data is a lot of work compared to normal write operations. In our city analogy, to allow a few once-occupied houses within a city block to be moved into, we must first move all of the tenants of the other houses on the city block to a completely different city block. Workers then have to go back to all of the houses on the city block and clear out of all the belongings before new tenants can move in. This extra work is what causes SSD performance to dramatically slow down over its lifetime, and it occurs when the drive is in use, further slowing performance.
So what have manufacturers done to avoid this slow-down? A technology called garbage collection was built into SSD controllers to help automatically reset the data blocks back to free space. Garbage collection will take the data pages from their current block and move them to a new block. This will then allow the old block to be erased and reset back to empty space. This process will ensure that there is free space readily available for new data to be written to quickly, without any extra erasing and moving steps. Garbage collection will move both valid data and invalid data (deleted files) from the old block to the new block. Garbage collection is a lot like having a moving company that moves all the furniture and people from their existing city block to a new city block. This process moves both the valid tenants (valid data) and the vacant house belongings (deleted data). The moving company then goes back to the old block and gets the houses ready for new tenants to move into. The garbage collection occurs when the drive is idle, so performance is not affected.
So where does TRIM fit in? TRIM is an operating system-based command for SSDs that is activated when you delete a file on the SSD. When you delete a file from your computer, TRIM notifies the SSD that the location of the deleted file no longer contains valid data. TRIM then works in conjunction with the SSD’s garbage collection process to move both valid and invalid data from the old block to the new block. Having TRIM enabled prevents the invalid data being moved. This in turn frees up space on the SSD and reduces write amplification. Now the “moving company” only needs to focus on moving the current tenants and ignore the vacant homes.
Apple added TRIM support in 10.6.8, but only for the SSDs they build into Macs. There are utilities and command line prompts available that hack the operating system to allow TRIM on other drives. While this can be beneficial for the majority of non-Apple SSDs that rely on TRIM to maintain their speed, performance, and reliability, it is important to remember that a hack in this context is the alteration of software that the original programmer did not intend to be possible. There is a risk of negatively impacting your computer and or data by enabling the hack, it can also be nullified through a future software update released by Apple. By enabling the hack, you are taking a gamble with your computer’s functionality and your data. This is another reason OWC does not recommend enabling TRIM on your Mac.
Now that we have an understanding of SSD basics, let’s take a look at what makes OWC Mercury SSD lineup stand out against the rest.
All OWC Mercury SSDs* have a SandForce Processor installed. SandForce processors improve an SSD’s performance and reliability. A key feature of SandForce processors is the DuraWrite technology. DuraWrite is a technology that helps reduce write amplification. As discussed earlier, write amplification is the act of data on the SSD being moved from block to block. Write amplification is expressed as multiples, based on how many times the data has been rewritten since it was passed to the SSD. This equation is calculated by taking the total amount of data written, then dividing it by the actual size of file. For example, a 2.0MB file is written to the SSD. Through garbage collection, it had parts of the file rewritten around the SSD totaling 5.0MB of data moved. The write amplification would be expressed as 2.5x.
DuraWrite helps reduce write amplification by compressing files that are written to the SSD. This compression can lead to write amplification that is less than 1x. Using the previous example, a 2.0Mb file that is written to an OWC Mercury SSD can potentially only take up 0.5Mb of space on the SSD. The write amplification would then be 0.25x. Compressing files means less data is written to the SSD which increases performance, reduces wear on the drive, and makes garbage collection more efficient. This is just part of what keeps an OWC Mercury SSD as blazing fast at the end of its life as it was its first day. We have even seen our drives perform faster over time!
Another feature of our SSDs is over-provisioning. Over-provisioning is reserving a portion of the drive’s total capacity for performance and maintenance tasks, and it’s the reason our SSDs come in non-standard capacities like 240GB instead of 256GB. The majority of OWC Mercury SSD have 7% over provisioned space. This additional free space available means that the SSD always has room to adequately perform garbage collection and won’t slow down even at its max capacity.
Through the DuraWrite technology, over-provisioning, and the garbage collection in the SandForce processer of our OWC Mercury SSDs, the need for TRIM is negated. If the firmware on your OWC Mercury SSD is up to date you can enable TRIM, but we’ve found no benefit in doing so since everything you need for top performance is built right in. Right from the start, the speed of your OWC SSD is stunning. It truly makes an existing Mac feel like it’s brand new again. And rest assured, you will enjoy that same speed for the life of that Mac and even beyond!
*UPDATE: Since this article was published, OWC has also released SSDs that use an equally impressive Silicon Motion controller.