I'm trying to figure out which read-only filesystem I should use to achieve fastest possible boot time in a stripped down embedded system using the Raspberry Pi Zero W (with the OS booting from the SD card).

cramfs and squashfs seem like good candidates, however I have no need to save space on the SD card and I'm concerned that decompressing the filesystem at each boot will slow things down.

Basic Linux permission and metadata support would be a plus as it will be used to mount the root system.

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    Decompression has a cost, but reading from flash has a cost too, and you do more of that when data is not compressed. To add to the confusion, SD performance varies wildly from model to model and brand to brand. There is no way to get a correct answer without benchmarking your specific hardware. – Oh My Goodness Jun 4 at 5:35
  • Yes I think you're right, a correct answer to this question will require actual benchmarks on a Rpi0w. Another thing to take into account is the ability to store the OS' critical boot data sequentially. I'm not sure that the model of the SD card would have a bearing on the relative performance of different filesystems though. – Jeremiah Rose Jun 4 at 9:33
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    The SD model matters because it determines whether the random I/O that's avoided with compressed data is more important than the CPU cost of decompressing a blob of sequential data. – Oh My Goodness Jun 4 at 12:47

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