User profile for user: Ian R. Brown
Ian R. Brown Author
User level: Level 7
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What is writing this large amount of data to my SSD?

I have been aware of the SSD wear controversy since the M1 was introduced so when I bought a base model M2 Mac mini a month ago I booted it from an old 1 TB Samsung T5 SSD with Ventura 13.6 installed.


I was expecting to take a performance hit but discovered that it was just as fast as using the boot drive in Geekbench tests and video editing with Final Cut Pro and Davinci Resolve.


Anyway, that's not a problem . . .


Yesterday I started up my M2 Mac mini, launched Activity Monitor. (I thought nothing was open but later discovered that Safari was on a default page)


The computer was left idling for under an hour and to my surprise I saw that Activity Monitor was claiming it had written 4.15 GB in that time although the individual items listed above totalled under 300 MB.



I put it to sleep for a couple of hours only to find that the Data Written was now 10.53 GB even though no apps were open apart from Activity Monitor.



This morning, over 13 hours later, the Data Written had risen to 11.5 GB although the changes to the individual items only added up to a few megabytes. The numbers don't appear to add up?



How can it apparently be writing this large amount of data when the Mac is doing nothing more than ticking over . . . or even less when it's sleeping?


You can understand my concern that even when sleeping it appears to be writing large amounts to the SSD . . . even though it is an external that can be quite cheaply replaced.

Mac mini, macOS 10.15

Posted on Nov 22, 2023 1:12 AM

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User profile for user: woodmeister50
woodmeister50
User level: Level 7
20,985 points

Posted on Nov 22, 2023 4:40 AM

Do you have TimeMachine enabled and is it doing hourly backups? If so, this could explain the initial disk writes being what they are and then when sitting for a long time at idle with nothing happening they decrease as there is nothing new to add.


Time Machine will not only write a backup to an external drive but it will also keep the last 24 hours of a backup locally in the system drive for easy recovery of files which is especially important with laptops or if the Time Machine drive is not available.


In addition, with Activity Monitor, the total disk writes are all disk writes to all devices attached to the machine. Here again, if using Time Machine, all its writes to the Time Machine Drive are included in that disk write total.


One more item, when your system is booted to an external drive, unless you intentionally access the internal drive, the internal drive remains idle and nothing writes to it or reads from it. So, all cache writes, virtual memory writes, etc. will be done on the externally booted drive and not the internal drive. Bottomline is that any wear and tear on an SSD when booted externally, will be on the external drive. What is unfortunate, is that external drive manufacturers generally will not spec a TBW (terabytes written) lifetime like they will spec on bare SATA or NVME SSDs.


I'm a bit long winded today but an additional thing to note using some math, say the TBW spec for a drive is 150 TBW which is a low side for 256GB SSD, writing 10GB to that drive every day means that you will not reach that mark for 41 years. Even at 30GB of writes daily it would be nearly 14 years before you would reach that number. With the rapid change in technology, your computer would likely be woefully outdated by then. Also, the TBW is an arbitrary spec made by manufacturers for warranty purposes and the SSD will likely last well beyond that amount.

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User profile for user: woodmeister50
woodmeister50
User level: Level 7
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Nov 22, 2023 4:40 AM in response to Ian R. Brown

Do you have TimeMachine enabled and is it doing hourly backups? If so, this could explain the initial disk writes being what they are and then when sitting for a long time at idle with nothing happening they decrease as there is nothing new to add.


Time Machine will not only write a backup to an external drive but it will also keep the last 24 hours of a backup locally in the system drive for easy recovery of files which is especially important with laptops or if the Time Machine drive is not available.


In addition, with Activity Monitor, the total disk writes are all disk writes to all devices attached to the machine. Here again, if using Time Machine, all its writes to the Time Machine Drive are included in that disk write total.


One more item, when your system is booted to an external drive, unless you intentionally access the internal drive, the internal drive remains idle and nothing writes to it or reads from it. So, all cache writes, virtual memory writes, etc. will be done on the externally booted drive and not the internal drive. Bottomline is that any wear and tear on an SSD when booted externally, will be on the external drive. What is unfortunate, is that external drive manufacturers generally will not spec a TBW (terabytes written) lifetime like they will spec on bare SATA or NVME SSDs.


I'm a bit long winded today but an additional thing to note using some math, say the TBW spec for a drive is 150 TBW which is a low side for 256GB SSD, writing 10GB to that drive every day means that you will not reach that mark for 41 years. Even at 30GB of writes daily it would be nearly 14 years before you would reach that number. With the rapid change in technology, your computer would likely be woefully outdated by then. Also, the TBW is an arbitrary spec made by manufacturers for warranty purposes and the SSD will likely last well beyond that amount.

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User profile for user: den.thed
den.thed
User level: Level 10
90,454 points

Nov 22, 2023 7:51 AM in response to Ian R. Brown

Ian R. Brown wrote:

The 2 mystery items are probably connected with software downloads that I thought I had disabled but it appears I had only partially disabled!

The 6.6 GB is suspiciously close to the 6.52 GB download of an update from Ventura to Sonoma. It looks as though that update could be sitting somewhere on my Mac. I wonder where and whether I could trash it?


Look in your Applications Folder for a macOS Installer(s), move to the Trash and Empty the Trash.

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User profile for user: BDAqua
BDAqua
User level: Level 10
250,253 points

Nov 23, 2023 5:54 AM in response to Ian R. Brown

AHA, if you just dragged those Apps to the Trash, they quite often leave /plists begging for attention.


You might have to Install those 2 again & use a good Uninstaller...


App Cleaner & Uninstaller, which is my goto cleanup app…


https://nektony.com/mac-app-cleaner


Mac Cleaner Pro...

https://nektony.com/mac-cleaner-pro


We need to see what all is running, a report from this will not display any personal info...

Using EtreCheck - Apple Community


EtreCheck is a FREE simple little diagnostic tool to display the important details of your system configuration and allow you to copy that information to the Clipboard. It is meant to be used with Apple Support Communities to help people help you with your Mac. It will not display any personal info.

https://www.etrecheck.com/


Thanks for Old Toad’s etrecheck instructions…

Slow iMac 2017 - Apple Community


Use the Note tool on the bottom of this editor's toolbar, as shown in the image, to copy and paste the output from EtreCheck. In a Reply before you click post, look for this to add longer texts...


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User profile for user: Ian R. Brown
Ian R. Brown Author
User level: Level 7
24,082 points

Nov 22, 2023 5:37 AM in response to woodmeister50

Thanks woodmeister50.


I am not using Time Machine.


I understand that I am being over-protective of my internal SSD but as mentioned, what shocked me was the figure of 10.5 GB written in the first 3 hours after boot when I was doing nothing at all on the Mac.


If it does that every day even before I do any work, it will soon eat into the TBW.


I have been told to look at "All Processes" and that revealed what was causing the bulk of the writing, particularly 2 weird things . . . the MobileSoftwareUpdater and StreamingUnZipService . . . what on earth are they and will they gobble up space every day?


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User profile for user: Ian R. Brown
Ian R. Brown Author
User level: Level 7
24,082 points

Nov 22, 2023 6:02 AM in response to Ian R. Brown

I have found the answers to my questions in the last paragraph.


The 2 mystery items are probably connected with software downloads that I thought I had disabled but it appears I had only partially disabled!


The 6.6 GB is suspiciously close to the 6.52 GB download of an update from Ventura to Sonoma. It looks as though that update could be sitting somewhere on my Mac. I wonder where and whether I could trash it?

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User profile for user: Ian R. Brown
Ian R. Brown Author
User level: Level 7
24,082 points

Nov 22, 2023 3:06 AM in response to hcsitas

I don't see how sleeping or not affects my problem which is the apparent excessive amount of writing done to disk whether asleep or idly awake?


The main puzzle is that in the first 3 hours after booting, AM claimed that 10.5 GB had been written but in the subsequent 13 hours overnight under 1 GB extra was added.


Furthermore the figures for the individual items listed above total only a few hundred megabytes and nowhere near the multi gigabyte figure given at the bottom.


Am I misunderstanding these readings somehow?


Incidentally, if I don't put it to sleep overnight, what should I do . . . leave it awake?

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What is writing this large amount of data to my SSD?

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