How Much Free Disk Space?

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bayswater
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How Much Free Disk Space?

Post by bayswater »

It's an old question. How much free space to you need on a Mac startup volume? I can find post which state with great certainty that you need 5%, 10%, 15%, 20% or 25%. And the answer is independent of the volume size which makes no sense to me.

The reason I want to know: I have a test partition and it currently has a High Sierra installation. I've installed a lot of stuff on it. At the same time, I've been trying out Symbolic Links to put libraries, samples, etc on another partition on the same drive. This has worked very well so far (If you want try this out, get Symbolic Linker 2.1.1. It operates as a service, and is the only thing I found that works consistently where aliases cannot be resolved.

At this point, I'd like to be able install a few other things on the test partition and then make it the regular startup volume because it represents a clean install. And I'd be able to keep my current Sierra startup volume as insurance for a few things that might stop working some time in the HS life cycle.

The problem is that this test partition is not very large. By moving lots of things via Symbolic links and relocating the user folder to another partition, I can install everything in about 65GB on a 85GB drive. I haven't tried symbolic links for plugins yet, but that might work as well, giving me another 6GB of free space (EDIT: it works. I tried a symbolic link for a few large plugins, and DP and Logic were none the wiser).

So: will 20GB of free space on an 85G startup volume be enough?
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FMiguelez
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Re: How Much Free Disk Space?

Post by FMiguelez »

That sounds totally fine to me. More than enough, actually. But I'd wait and see what Mike says about it...
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mikehalloran
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Re: How Much Free Disk Space?

Post by mikehalloran »

Can I answer without explaining? OK.

What’s the difference between a 1T SSD with 960G free and another with 1T free? They’re the same size — it’s that the NAND Controller firmware reserves less space for over-provisioning from 15% (960G) to 7% (1T).

It seems that Samsung and others decided that, with TRIM, drives didn’t need as much free space as was thought.

The Controller does not make this free space available. Technically, you can fill the drive up and not touch it.

But wait. There’s more. APFS screws with everything. Apple has yet to write the White Paper explaining how it works. If you think of it as being able to have virtual partitions sharing the same space, you wouldn’t be wrong.

I can tell you what doesn’t work: creating partitions and then reclaiming the space when you’re done as you are used to in Disk Utility. If one partition is APFS and the other isn’t, it’s pretty easy. It’s multiple APFS partitions on the same drive that is a major PIA until Apple updates Disk Utility. If you can avoid that, do so.

You won’t be able to view your APFS partition from Sierra. To switch, you will shut down and Option-boot, then select the drive you will boot into. As I did this morning when I updated my El Cap drive then went into my main drive. BTW, you’ll do the same going between APFS drives more often than not.
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bayswater
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Re: How Much Free Disk Space?

Post by bayswater »

I have no SSDs on this system and no APFS volumes. It's an old iMac that requires major surgery to replace the drive. Otherwise I'd have put a huge drive in it a while ago, probably an SSD. I'm not changing any partition sizes. I have a 250G partition that currently runs Sierra and is the current main startup volune. There is another 85G partition used for testing new OS versions that now has High Sierra on it. The third partition has samples, libraries etc and will remain static. I just want to use the small partition as the startup volume with about 60G of stuff on it, and about 20G of free space, and not get problems because of too little free space.
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Re: How Much Free Disk Space?

Post by mikehalloran »

The only difficult part of changing the drive on your iMac is if you also want to change the NV RAM battery at the same time. The process is identical to changing mine which I did twice: once to install a 1T 845 EVO and again to change it to a 2T 850 EVO. You don’t need to remove the screen nor disconnect the bezel wiring. Removing the glass is easy with suction cups but Guitar picks work, too — it’s held on with magnets. I really have done it one-handed—not by choice as those who have met me can vouch.

Changing the battery does involve removing the motherboard. The 2009–2010 were unique in that regard. Seeing that I needed to use 2 hands, I took it to a local tech and gladly paid the $75 he wanted. Had I known, I’d have let him do the whole job since replacing the drive would have taken 2 or 3 minutes longer once the screen was loose.

Besides the SSD, you need an inexpensive bracket and a replacement heat sensor from OWC that allows any replacement drive, HHD or SSD. They still have the one for the 2009–2010.

You’ll have a new Mac. Besides being faster, it will run cooler and quieter as the fans have far less work to do.
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bayswater
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Re: How Much Free Disk Space?

Post by bayswater »

mikehalloran wrote:The only difficult part of changing the drive on your iMac is if you also want to change the NV RAM battery at the same time.
----
You’ll have a new Mac. Besides being faster, it will run cooler and quieter as the fans have far less work to do.
I've watched the movie twice but I don't like doing something like this unless I've had a spare to work on first. But this is plan B if nothing good appears from Apple in the new year, and a PC doesn't work out. But, seems to me I'd have to change the battery on a Mac this old, so I'd probably take to some one else to do the work.

Meanwhile, do you have a view on free space?
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Re: How Much Free Disk Space?

Post by mikehalloran »

The movies tell you to take everything apart which is not necessary as I found out. Steps 1–5 at ifixit.com allow you to lift the top of screen high enough to replace the drive—I prop it up with the box from the SSD. Then you have plenty of room to follow 10–14 to replace the drive in the bracket.
https://www.ifixit.com/Guide/iMac+Intel ... ement/1634
Steps 6–9 are the ones that get people in trouble and are unnecessary if just replacing drives. The screen needs to be removed only if you are then going to remove the motherboard below it to replace the NV RAM battery.

The cautions regarding the OE heat sensor are outdated as you cannot buy drives that reuse it. The OWC sensor for the 2009–2010 iMac is needed for any replacement drive. Not using it in favor of the so-called software solutions will have most tearing it down again in a week to install that sensor.


I go with the standard reccomendation of >15% free space on HHDs. They do slow down once you go under that.

With SSDs, you want enough free space to allow for upgrades. If you were to hit capacity during an OS upgrade, it could lock your system forcing you to wipe the drive, do a Time Machine Restore, free up some space and try again. This is a time consuming PIA. I tell my customers that 5% is a safe margin. 2% on a 1T is too little for me — on a 2T, it could be a safe margin, I suppose.
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bayswater
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Re: How Much Free Disk Space?

Post by bayswater »

I've got in excess of 20%, so I guess I'm OK on that item. At a dead end for now though. A few apps I want to install are not "acceptable" to HS. Patches are available, so it's a matter of time.

Mike, did you put HS on your iMac? If so, did you notice a firmware update? I heard the tell tale chime. SInce this, the iMac is unable to change startup volumes in one pass. I have to change the startup volume, restart or do a cold start, wait for the Mac to freeze up, power off, and start again. It always fails on the first startup after changing the startup volume, and alway succeeds on the second attempt.

HS on the test partition has also affects Spotlight on the Sierra partition. When in Sierra, spotlight searches always result in hits on the HS partition. I used to use spotlight to launch apps in Sierra. It's useless now -- it never finds Apps on the active partition.
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