[marcan_42]

The worst example we have so far shows 3% lifetime usage in 2 months, on a 2TB model. Since the total lifetime write spec normally scales with SSD size (these things are usually specced in "drive writes per day" for a given fixed lifetime for that reason), assuming this excessive write volume issue itself does not scale with drive size, a 256GB SSD model would be at 23% lifetime usage under the same conditions, or about 100% in 8 months.

Even if you just look at the 2TB model itself, 3% in 2 months means the thing will reach 100% in 5 years which is... not great.

So there is reason to be concerned here.

[supermatt]

Instead of "assuming", I checked my machine. I have a 256GB version with 8GB RAM. I received it 3 days after launch, and it has been used consistently for iOS, android and web development. It is showing 1% "Used" - the same figure as the OP. Im not sure where you are getting 3% from.

[marcan_42]

Please don't judge me (OP) by the HN submission title, which is not at all an assertion I made. Nobody ever said "most" machines are affected.

This is the worst example so far, 3% on a 2TB SSD.

https://twitter.com/david_rysk/status/1361155414994407424

Care to share the actual write volume that corresponds to 1% used for you on your 256GB drive, so we can validate whether the linear scaling by drive size assumption is reasonable?

[supermatt]

  SMART/Health Information (NVMe Log 0x02)
  Critical Warning:                   0x00
  Temperature:                        32 Celsius
  Available Spare:                    100%
  Available Spare Threshold:          99%
  Percentage Used:                    1%
  Data Units Read:                    42,513,003 [21.7 TB]
  Data Units Written:                 35,670,814 [18.2 TB]
  Host Read Commands:                 444,309,142
  Host Write Commands:                237,126,099
  Controller Busy Time:               0
  Power Cycles:                       213
  Power On Hours:                     199
  Unsafe Shutdowns:                   13
  Media and Data Integrity Errors:    0
  Error Information Log Entries:      0

[marcan_42]

The SMART info does not include the drive size, which was an omission in my request for info tweet which I regret :)

So 18TB / 256GB = 70 drive writes is 1%.

For the 2T drive, we had 150TB = ~50 drive writes being 3%.

So, it seems this isn't linear after all. But it's also not constant; 150TB would put you at 8% used on your 256GB model with this scaling (instead of the ~23% if it were linear), which is still not insignificant, and would still get you to 100% within a couple years. Though there is significant rounding error with the "1%" figure.

I saw someone else mention 3% on Twitter too and asked for their drive size, so I hope that can give me another more accurate data point.

[supermatt]

I just assumed that this was some deep "app nap", where its effectively swapping the entire state of an inactive app to disk. That would likely explain why the usage is scaling with available RAM, rather than storage space.

I get that its a much higher wear than we would traditionally expect, but given I have 8GB of RAM that seems near inexhaustible., maybe it just a different approach to memory management, permitted by the blazingly fast storage we now have access to? I simply couldn't run all this stuff on my 16GB 2015 machine.

I cant run figma though - that thing eats 4GB for a smallish project, so it almost always complains about my available memory when im using figma.

[marcan_42]

So, going back over the numbers and with a 256GB 3% user confirmed on Twitter, it seems like the ratings are:

2TB model: 5000TBW

256GB model: 2000TBW

That means that, at the worst known rate that David had (150TB in 2 months), a 256GB drive would reach lifetime writes in ~2 years. That's still way too fast, so this is still something Apple needs to adjust if it is happening to people (and given what he told me about the write rates he was seeing while using and switching apps, it really does seem like a bug, not normal app swapping).

FWIW, the "app nap" thing is what iOS does, but macOS can't do that because Mac apps aren't really designed that way. macOS just does traditional swap plus compression, as far as I know.

[rasz]

"Percentage used" might be as accurate as Cellphone reception bars. What is really important is the

    SSD capacity * ~600 / Bytes written 

and quality of wear leveling firmware in Apple SSD.

[supermatt]

Maybe so, but it’s the figure manufacturers use in their warranty