Aligning an SSD is the process of ensuring that your filesystem’s logical blocks begin and end on the same memory boundaries as the SSD’s memory blocks. Doing this improves speed and longevity. Not doing it can roughly halve your drive’s life expectancy.

It’s not as mysterious or weird as it may seem. I’ll try to take the mystery out of it.

Why alignment matters

align SSD

Be sure to align your new SSD to ensure you get maximum performance and life expectancy from it.

A traditional hard drive just writes data in chunks–whether they’re 512 bytes or 4K depends on the drive–and doesn’t care how you do it. An SSD is made up of memory cells 4K in size, and since those cells can wear out over time, an SSD does care how you do it.

Your operating system’s filesystem splits up data into chunks that are a nice, even multiple of 1K. If the filesystem’s boundaries line up with your SSD’s 4K boundaries, everything’s great. But if they don’t line up, the SSD has to write onto two 4K memory cells. How much this slows operations down depends on the SSD–with some drives, the slowdown is negligible. And even if you have a badly misaligned SSD, it will still be much faster than a platter drive, so you may not notice or care.

But here’s why you should care: It will decrease life expectancy since the drive is actually writing twice as much data as it would otherwise. This is called write amplification, if you care to know. And personally, if I pay $200 or more for a large SSD, I don’t want to do anything to it that will decrease its life expectancy. I want it to last the promised 5-10 years.

How to align an SSD

Aligning an SSD is a fairly straightforward process that shouldn’t take too long–less time than you’d spend defragmenting a traditional hard drive–and you can accomplish it entirely with software that doesn’t cost anything. See how to align your SSD or RAID array for free.

If your drive included software to clone your old drive to your new one, it may very well have aligned the drive during the cloning process. And if you installed Windows onto a freshly formatted drive, it aligned it. But under any other circumstances, there’s a good chance your drive isn’t aligned. Here’s how to check. That won’t cost you anything either.

Here’s another trick: Make sure AHCI is enabled (scroll to the end of the link). Enabling AHCI allows functionality like NCQ and TRIM to work.