How necessary is it to reserve 15% disk space?

Viro

Viro

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I read the thread at http://www.macfixitforums.com/php/s...570808&page=0&view=collapsed&sb=5&o=7&fpart=1

It seems to be written by someone who works at Micromat and he/she claims that you need to reserve 15% of your disk space free or else your disks might get corrupted.

I've never heard of such a thing with other file systems and it instantly makes me suspicious that HFS+ would be so ... unreliable. Anyone know how reliable this information or if there are any official documents from Apple that support this claim? 15% of my hard drive is 9 GB which is a *lot* of wasted space.
 
I have heard a few different sizes, I think I have a MacWorld somewhere that says 8%. The only thing I can think that this would be used for is swap/vm space.
 
Yes, a few GB is useful for temporary data your system is generating. It is not a question of % but an absolute value. And the 5GB are of course needed to burn a 4.7 GB DVD !!!

The more programs you open at the same time, the more free space you need.
 
That's all fine and helpful, but how much space is necessary? 2x RAM? 8% hard drive capacity? 15%? I've got so many different responses and I'd like to know which is accurate.

Btw, I don't burn DVDs so I don't need 4.7 GB free, thankfully.
 
In this case, as long as you stay above 1 GB you should be ok. But this depends on the software you use... as the programs are the ones who reserve size for virtual memory. You can check your memory usage with the Activity Monitor (in Utilities folder). Right now I have 4.7 GB of virtual memory open, 700 MB for the system, 400 MB for Firefox, 200 MB for the windows server, 12 other thread use between 100 MB and 200 MB each (System server, Skype, Finder, Mail, Safari, ...). If you have less HD available, virtual memory will be reduced and data will need to be created again more often (the nice rotation beach ball, you know...).
 
2 or 3x RAM is a good place to start. Depending on what programs you use, that might be enough or not. If it's not, you'll get warning messages that you're starting to run out of disk space.

Master of Orion 3 burns through swap space like there's no tomorrow...
 
Personally, I keep at least 25% free. The number you pick, of course, would depend on your HD/system config and the stuff/apps you run, but I'm figuring on a 40GB one with the iBook. 25% or more free, the iBook runs great. Slightly slower down to 15% or so, then anything less and it slows down noticeably.
 
Viro said:
I've never heard of such a thing with other file systems and it instantly makes me suspicious that HFS+ would be so ... unreliable. Anyone know how reliable this information or if there are any official documents from Apple that support this claim? 15% of my hard drive is 9 GB which is a *lot* of wasted space.
Click to expand...
That is a very real safety limit. And what is worse, I've seen (and had to repair) the damage caused by not following that limit.

It is a soft limit though. You can run at less than 15%, but I wouldn't do it for very long. And if you are running at less than 5% I would suggest making sure you have your data backed up.

The types of problems that come from this are in the HFS catalog section of the disk. They can make a disk unmountable or even strip away the hierarchal file system (basically explode all the folders so all your files are on the root level of the drive).

It is not fun to clean up, and you may need expert help in salvaging the info on the disk. At any rate, reformatting is the only real way to bring the disk back to a completely usable state.

As for how long this 15% free space limit has been around, it has been well known in the Mac service community for years (I first heard about it in 2000). My first experience with it came in 2001 with an AppleShare IP system that was running at over 97% full for a few weeks. As it had exploded tons of flight checked QuarkXPress project folders on an 80 GB drive, most of those folders were never put back together.
 
With the price of external HDs so low (and dropping each day), space shouldn't really ber a problem.
After ram, I'd say the second-most important aftermarket purchase should be an external for backups and saving space. (iPods are also good for this).
 
Great..... so the danger is real. My 60 GB drive has about 21 GB free at the moment so the danger isn't imminent. However, if I were to add more stuff to my machine, I'll need more space since in reality if we took into account the 'safety limit' I actually have about 12 GB free!

Looks like I have to look into buying one of those 100 GB laptop drives. Or move to another OS that doesn't use such a bad FS ;).
 
Because that'll mean I need to lug an external drive with me. It works most of the time, but then there could be stuff on the external drive that I need but I forgot to bring along if I went to a conference or some far out place.

I've got a 60 GB external drive at the moment, and I'm only using that as a backup solution.
 
You have a 60GB drive and you're worried about not having enough room? What are you keeping on it? Video? Music?
 
I have never heard of a magic number. Certainly 5GB of space is a safe bet. I keep just what i need on my PB and everything else is on my external. An external drive, in my opinion, is necessary for a laptop owner.
 
Randman said:
You have a 60GB drive and you're worried about not having enough room? What are you keeping on it? Video? Music?
Click to expand...

Well, I've got quite a bit of videos in DV format since it's uncompressed and there aren't any key frames that will just wreck the experiments that I run. This is easily about 10 GB. And it goes up quite quickly when I get new videos, but I can easily store these on external backups. Even so, there's a lot that still needs to be on my laptop when I go to conferences/workshops and demo them.

Then there's my development tools, which include MATLAB, Netbeans and Eclipse, and tonnes of documentation. Adds about 2 GB. Lots more applications that I can't just dump.

Then there are the games :). Ideally, I won't want to ditch these as they take a long time to install.

But yeah, I've got 22 GB free at the moment. But the hard limit means that really have about 13 GB free. Guess I'm just itching to have loads of free space.
 
Ah, the games. Now we are getting somewhere. Do you have an iPod? Either store stuff on it, or keep your music on the external (made bootable via CCC) and you can save space.
 
Nope. No iPod, but I have an external drive. For now, I'll just move my games to the external drive and run those from there.
 
This is why I would never run OS X as a production server that I relied on to make a living - if the log files can steal my swap space, this is a real problem.

Now, I've never worked with OS X server. Maybe it has the option to partition things so that, for example, /var/vm and /var/log are on different partitions. I don't know...
 
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