I've read a few things here and there about hard drive cluster sizes and how it can help get more space out of a hard drive if the cluster size is set to maximum in case of very few very large files (databases, I presume). Those sources usually mention Linux and server usage. But what about a home computer on Windows?

I think it's possible to figure out how much space you can free up if you change the cluster size on any existing hard drive, but I'm not sure what it would mean for IO performance. Some sources mention that certain hard drives are optimized for standard (4K) cluster size and will read/write significantly slower if it is changed.

Is there a tool or some way to test if changing cluster size of one of your hard drives would improve performance and/or free up a bit of space?

2 Answers 2


you would need to reformat the hard disk with the new block size, and then reinstall the OS. The new install is then always slightly different from the current one, so it would be hard to even measurable if there was any gain, in performance as well as in disk space.

Any effect would be minimal if at all. If you are really sweating for 1 or 2% space savings, you can try it, but don't expect anything more. If you want the machine faster - aside from buying a faster PC - you could exchange the hard disk for an SSD. That is the same installation effort as trying to change the block size, but will have a significant effect (but it costs money)

  • I actually have an SSD for my OS drive. Would a non-standard block size change anything on it? Jan 22, 2016 at 3:12
  • SSD have no blocks size. They are physically differently built, there is nothing that you can do to configure it faster or different.
    – Aganju
    Jan 22, 2016 at 3:20
  • @Aganju SSDsare even more sensitive to a misconfigured filesystem allocation unit size. Windows will use the safest options which work 90% ofthe time. If you want to really try to get the SSD filesystem perfect, you must look for the erase block size of the SSD at the very least, and try to align the allocation unit size to this size. Use the linux tool github.com/bradfa/flashbench to try to measure the SSDs physical properties. note YMMV.
    – Hydranix
    Jan 22, 2016 at 4:28

You can't change the hard disks block size. It's determined by the physical properties of the disk.

You probably mean the filesystem block size. In Windows parlance this is called "cluster size".

Increasing the block size will never allow you to store more data on the drive. Decreasing the block size can allow more data to be stored on the drive, but it is only even slightly meaningful when you have a very large amount of small files.

Block size optimizations are made more for the performance benefit that occasionally can be made in very situational circumstances.

You cannot change a filesystems cluster size. You must set it when you format the media.

For your case of a few large files on a disk, your best bet is to ensure that the files are contiguous (not fragmented) by defragmenting the filesystem. Then you can access the file linearly, playing to a hard disks strengths.

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