How does block size affect performance

Microsoft Windows and other computer operating systems manage hard drive space by dividing it into equally-sized units called clusters or blocks. Over time, however, a drive's block structure becomes fragmented, reducing file processing efficiency. The size of the blocks affects the degree to which files become fragmented. Although bigger blocks reduce fragmentation, they hamper efficiency in other areas.

When you delete a file, Windows marks its blocks as available. Upon creating a new, larger file, Windows reuses freed-up blocks, then hunts for more blocks elsewhere on the drive to make up the difference. The file is fragmented because not all the blocks are in one place. As your computer deletes and creates files, the new ones tend to become more fragmented.

Conflicting requirements determine ideal block size. As blocks become bigger, more files consist of a single block, reducing fragmentation. Stack Overflow for Teams — Collaborate and share knowledge with a private group. Create a free Team What is Teams?

Learn more. Will a large block size affect speed noticeably? Asked 6 years, 9 months ago. Active 6 years, 9 months ago. Viewed 3k times. Improve this question. Spindle hard drive or SSD?

I assume that's what you're asking. Related answer to the inverse question : Downsides of a small allocation unit size — sawdust. Add a comment. Active Oldest Votes. When I fish out some benchmarks to back this up I'll add them here. You should look up how flash storage works in units of Pages and why any flash based storage requires a garbage collection process. Sign up to join this community.

The best answers are voted up and rise to the top. Stack Overflow for Teams — Collaborate and share knowledge with a private group. Create a free Team What is Teams? Learn more. Ask Question. Asked 3 years, 4 months ago. Active 3 years, 3 months ago. Viewed 15k times. I was reading about superblock at slashroot when I encountered the statement Less IOPS will be performed if you have larger block size for your file system.

Now my question is how much more IO would disk A need?. So who is deciding what is the size of the IO request? Is it equal to the block size? Some people say that your application decides the size of IO request which seems fair enough but how then OS divides the single request in multiple IO.

Is it possible that in both disk A and B the data can be read in same number of IO? Does reading each block means a single IO? If not how many blocks can be maximum read in a single IO? If the data is sequential or random spread, does CPU provides all block address to read once? Improve this question. Ankit Kulkarni Ankit Kulkarni 1 1 gold badge 2 2 silver badges 6 6 bronze badges. Add a comment. Active Oldest Votes. I think the Wikipedia article explains it well enough: Absent simultaneous specifications of response-time and workload, IOPS are essentially meaningless.

Now to your questions: So who is deciding what is the size of the IO request? That is a both an easy and a difficult question to answer for a non-programmer like myself. As usual the answer is an unsatisfactory " it depends "