3 ms·
Hard drives generally use a fairly simple linear mapping between LBAs and physical location. Low LBAs are on the outer edge of the platter where transfer speeds
by wtallis 7y ago
Hard drives generally use a fairly simple linear mapping between LBAs and physical location. Low LBAs are on the outer edge of the platter where transfer speeds are highest, and high LBAs are on the inner edge where speeds are lowest. Unlike SSDs, hard drives don't need wear leveling, so there's no reason to break from that pattern except in the relatively rare instance of damaged sectors.
At smaller scales, the layout of individual tracks can vary quite a bit, but that doesn't have as much impact on overall sequential transfer speed. See http://blog.stuffedcow.net/2019/09/hard-disk-geometry-microbenchmarking/ http://blog.stuffedcow.net/2019/09/hard-disk-geometry-microb...
- zozbot234 7y agoYour link was discussed @ https://news.ycombinator.com/item?id=21492345 https://news.ycombinator.com/item?id=21492345
- wtallis 7y agoYep. I found it interesting enough to bookmark, and now I tend to pull it up when somebody wants to know how hard drives really work.
- mehrdadn 7y agoLow LBAs are outside rather than inside?? I had no idea.
- wtallis 7y agoIt stands to reason. The low LBAs get filled first and used most. The outside of the disk is where the linear speed is fastest, and it's closest to where the heads park.
- mehrdadn 7y agoYeah I understood that immediately after I read it, but it's not how typical optical discs work, and I'd just assumed they work the same way until now. Hadn't really thought about it before. What I find a bit bizarre though that some defragmenters have an option to move files to the end of the drive. Wouldn't you want to move files to the beginning in that case?
- kalleboo 7y agoMaybe if you're optimizing for write performance of new files (e.g. back in the day when sequential disk performance was more of a bottleneck, you'd want lots of contiguous free fast disk space for something like digitizing video)