The Fuller a Hard Drive Is, the Slower It Goes

For many years, I’ve written that the fuller a spinning hard disk drive (HDD) is, the slower it goes. But, while I’ve “known” this for years, I never really bothered to test it. Until this week, as part of a detailed review of a Thunderbay 4 HDD RAID.

The short answer: It’s true. Hard drives slow down as they fill up.

As this chart illustrates, speed reductions can lower performance by a third!

The general rule of thumb to maintain consistent performance is to keep available (free) space to 20% or more.

To see how much free space you have on your storage, double click the drive to open it, then look at the Available Space numbers at the bottom. Try to keep these about 20% for all HDD storage.

• NOTE: This rule does not apply to SSDs, only HDDS.

If you don’t see storage volumes on your desktop, go to Finder > Settings > General and check all four options included in the red box above.

EXTRA CREDIT

• This PDF contains all the details from my tests.