A thought about HD sizes and minimum needed disk space

Question

This has just occurred to me and I am looking for more accurate numbers to help advise posters here, more accurately, when the situation occurs.
In this day and age of Macs with 500 Gigabyte and 1-4 Terrabyte drives, do we still need to tell people that have filled up their Macs' HDs that they need to leave 15-20 % of the total drive size free for OS X to still work properly.
Because this, actually, equates to a mimimum of 100 Gigabytes to, at least, 200 Gigabytes or more, for larger drives, of drive space that needs to be cleared of data! Just to have enough drive space for OS X?
Does anyone else thinks that this is a ridiculous amount that OS X, by itself, actually needs to run smoothly?
Does anyone here have a better estimation of just how many GBs OS X uses on an average basis?
I would rather have a more realistic size to have remaining on a hard drive than to keep using the percentage rule.
I know the percentage rule was used in the day when we had smaller capacity drives, so it would still apply in those situations.
But I do not think it no longer applies when drive capacities are so much larger today and getting larger.
Any thoughts and more realistic numbers welcome.
I am going to post this also, in the Mac Pro section.

Answer 1

Yes, going by percentage is just plain silly. Here is  the most intelligent comment on the subject I've seen (from Anonymous at XYMer's.) Btw, he wasn't recommending keeping a minimum of 75GB free. The 75GB figure was in response to someone who asked if that was adequate. 75GB was what happened to be free and it would appear it was far in excess of what was really needed.
Here's a link to the full discussion
http://x704.net/bbs/viewtopic.php?f=9&t=6004
These suggestions, so far as I can tell, have neither theoretical nor empirical basis. They're sort of like the advice that you need to always drink at least 12 glasses of water per day: someone said it once, and since then it has taken on a life of its own.
You really probably should keep some drive space free. If you have 75 GB free, you're fine. The amount that you might want to keep free could perhaps best be described as, "enough to hold everything without any fear of unexpectedly filling up." For comfort I'd set aside about 6 GB for virtual memory, but that number will vary vastly depending on how you use your computer. On top of that I'd keep several GB to leave room for the system to move files around, and maybe another half dozen GBs just in case I need to store something large or something unexpected. So I'd be shopping for a new hard drive or cleaning up big files well before space went below 16 GB. In reality, I wouldn't wait nearly that long, because I could extrapolate based on usage that I'd be getting uncomfortably full well in advance of it actually getting that full.
On the other hand, I have one machine that never really gets files added to it, that I keep with only a couple GB free because it causes no problems based on the way I use it and there would be no benefit in increasing the available space.
To be clear, nothing bad suddenly happens when you cut below some magic number. Rather, depending on how you use your computer, you may experience minor to noticeable performance degradation as free space approaches zero. The dynamic pager, for example, likes to create virtual memory files that dynamically double in size each time one is created, up to a maximum of 1 GB. If there's not room to create the file it wants, your computer could slow down or seize up. Likewise, if you're running very near the drive capacity, bulk writes could slow down because there may not be large contiguous sections of disk available. But you'll generally need to be really close to the edge to notice.
Back in ye olden days of teeny tiny drives, any particular file would take a greater percentage of available space, so it was on average more important to keep a larger percentage of the drive free. But to reiterate, how much space you have free doesn't really matter as long as there's enough of it that there's no danger of it suddenly filling up.
- Anonymous
Message was edited by: WZZZ