Comment by rowanG077

4 years ago

You think it's oke that restarting your PC leads to data loss or corruption? That's basically a product killer for me. I reboot my laptop everyday.

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rowanG077

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marcan_42  4 years ago

You presumably don't reboot your laptop by connecting a USB-PD gadget that issues a hard reset. A normal OS reboot is fine, that will flush the cache.

The most common situation where this would affect laptops, in my experience so far, would be a broken driver causing a kernel lockup (not a panic) which triggers a watchdog reboot. That situation wouldn't allow for an NVMe flush.

  • signal11  4 years ago

    For products like the Mac Mini, which don’t have a battery, does this mean that a loss of mains power will cause data loss? Because brownouts do happen occasionally…

    • marcan_42  4 years ago

      Yes. I've tested yanking the power and can easily see 5 seconds of data loss for data that was fsync()ed (but not full synced). I'm not sure yet if corruption due to reordering is also possible, but it seems likely.

  • rowanG077  4 years ago

    Depends what exactly is a hard reboot. I don't reboot my laptop by issueing USB-PD command. But I do by holding the power button.

    • marcan_42  4 years ago

      I just tested that. Holding down the power button invokes a (somewhat special) btn_rst kernel panic before it has a chance to invoke a true hardware reset, and kernel panics involve an NVMe driver hook which I'm pretty sure issues a flush. Should be safe.

      At least re: this issue; it's still a bad idea because it's only safe if all software is written following data integrity and flush rules to the letter, and most software isn't. You're eventually going to run into issues on any OS by doing that, because most software doesn't get this right unless it's a database. And you're still going to lose data that's in buffer cache, I'm pretty sure that won't get flushed.

    • Cthulhu_  4 years ago

      See, that's a forced shutdown, a last resort measure; it's using a sledgehammer to tap in a nail. You shouldn't do that as a habit, even if this particular optimization issue wasn't a thing.

      I mean I grew up diligently turning off my PC by parking the disk and using the various operating system level shutdown procedures. Nowadays I smack the off button, but that still just triggers the OS shutdown procedure. I don't turn my Mac off as a rule, its sleep mode actually works. ish.

Bud  4 years ago

1) A normal restart doesn't have this issue, at all.

2) Why are you rebooting a laptop daily? My uptime on my MacBook Pro averages 30-60 days. There's zero reason to reboot any modern OS daily.

  • lobocinza  4 years ago

    > There's zero reason to reboot any modern OS daily.

    - I use Arch, I like to avoid accumulating too much major updates between reboots. - For a time I was facing a bug that resulted in a black screen of death after resuming sleep.