OS X writes more than it reads (7GB in/out in 23 hours, most of it from OS X)

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OS X writes more than it reads (7GB in/out in 23 hours, most of it from OS X)

In my previous question, I mentioned that OS X seems to really like writing to the disk.

Everything in green are my comments.

Specs: EtreCheck version: 2.1.8 (121)

MacBook Pro (Retina, 15-inch, Mid 2014)

MacBook Pro - model: MacBookPro11,3

1 2.5 GHz Intel Core i7 CPU: 4-core

16 GB RAM Not upgradeable

BANK 0/DIMM0

8 GB DDR3 1600 MHz ok

BANK 1/DIMM0

8 GB DDR3 1600 MHz ok

Bluetooth: Good - Handoff/Airdrop2 supported

Wireless: en0: 802.11 a/b/g/n/ac

Battery Health: Normal - Cycle count 21 (yes, this laptop is still new)

You don't understand how baffling it is to me that OS X can write 1.5 GB to the disk while reading a grand total of 16 MB over the course of 23 hours. Yes, this rMBP has been up for barely a day, and OS X has managed to write 7 GB to my poor, poor SSD.

As you might see, with 23 hours of uptime, OS X managed to write a grand total of 7GB to my SSD. My poor SSD, I hope you last for long enough for me to fix the problem with OS X.

When you write stuff to disk, it generally means that you want to store it there at retrieve it at a later time. But, not for the almighty Apple. Here, we write 2 GB to your hyper-expensive SSD, while we only read 200MB of anything. Heck, because I can't attach anything to the kernel, I don't even know what on earth kernel_task can be reading!

If I attach fs_usage to any of them, all I get are HFS_update, which my limited knowledge of HFS tells me that is not a major contributing factor. (how much can you write to a disk with filesystem updates? I know I come from the nice linux world of ext4, but filesystem updates writing several GBs to disk seems unlikely)

So, if anyone can tell me what on earth nsurlstorage, kernel_task, and launchd are writing to disk, and how I can potentially decrease that value, I will greatly appreciate it. I would also appreciate it if someone can explain to me why there are 2 instances of cfprefsd. (how many daemons for whatever cfprefs is do you need?)

MacBook Pro with Retina display, OS X Yosemite (10.10.1)

Posted on Mar 6, 2015 7:57 AM

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Answer 1

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John Galt

Level 10

141,296 points

Mar 6, 2015 8:55 AM in response to abstruselyarcane

My poor SSD, I hope you last for long enough for me to fix the problem with OS X.

There is nothing wrong with your OS X installation. That's the way it works. If its activity troubles you, return your rMBP for a cash refund that you can use to build yourself several nicely-equipped Linux boxes.

There is no way to disable what OS X is doing without resorting to system "hacks" that this site does not generally tolerate and that I would not recommend anyway. For an in-depth explanation you'd be better off asking your question on stackexchange or similar technically-oriented site, but you ought to know you're seeking to fix something that isn't broken. Good luck!

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Answer 2

Mar 6, 2015 9:07 AM in response to John Galt

There is nothing wrong with your OS X installation. That's the way it works. If its activity troubles you, return your rMBP for a cash refund that you can use to build yourself several nicely-equipped Linux boxes.

The problem with linux is that they are great for servers, but terrible for everyday laptop use (but still better than Windows). I have really learned to like OS X, just that all of its weird quirks with how everything works makes my inner nerd cringe at the thought of my system being the way it is.

It is just that it strikes me as odd that the core system services would need to write this much data to the disk. What's the point of writing stuff to disk when you are not going to read it later? They are probably not backups, because it makes no sense to put backups on the same disk.

you ought to know you're seeking to fix something that isn't broken. Good luck!

I was under the impression that this is abnormal, which is why I asked here. I guess I will post something on the apple stack exchange about this, but if this is normal, I might just close this thread. Sorry to bother with everyone's time.

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Answer 3

John Galt

Level 10

141,296 points

Mar 6, 2015 9:14 AM in response to abstruselyarcane

Most of the data can be attributed to Spotlight indexing, which enables a Mac user to search its contents (including the contents of certain file types) extremely quickly. It writes most of that upon initial configuration or upgrading OS X. After that, only incremental changes are written, but it's still going to account for a fairly large aggregate amount. You can exclude designated files or volumes from the Spotlight database using its Preferences, but I don't recommend disabling it entirely. Once it finishes building its index, its effect on performance is negligible.

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