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    Both 32-bit and 64-bit Linux kernels use default dirty_ratio of 20. However, 32-bit kernel has maximum available kernel RAM limit of 1 GB due to limits of 32-bit x86 architecture. As a result, maximum default write cache size on 32-bit system is around 180-200 MB depending on hardware (at least PCI devices with DMA access will reduce usable RAM limit). Commented May 17, 2017 at 7:18
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    This isn't the complete answer to your original question though. I want to throttle my external slow storage, not my internal fast storage... Commented Apr 9, 2020 at 18:27
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    Decreasing the write_buffer size below the current utilization may lead to a somewhat unresponsive system, as it appears new writes are blocked until space is available in the cache, which is now overfull. Creating a directory in this state has left me enough time to clean up a kid's toys in the yard, cut a slice of key lime cheesecake and a glass of milk, and finish both while I write this from my phone. Commented Aug 28, 2020 at 1:35
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    After using low dirty_bytes setting (200 MB) for a longer time, I've noticed that using single global limit is pretty bad because slow device can still fill the buffer and then writes to another fast SSD device suffers as a result. The correct fix is to apply device specific limit but there doesn't seem to be a simple way to do that. I think optimal setting would be 200 MB per device for my case. Commented Aug 18, 2022 at 6:46
  • See also: unix.stackexchange.com/q/714267/20336 Commented Aug 20, 2022 at 10:22