Block Size When Installing to Compact Flash

  • Page 34 of the pfSense Book talks about installing pfSense onto a compact flash card using the dd command. I noticed that the example invocations of dd use block sizes of 16k, 64k and 16k for Linux, FreeBSD and Mac OS X, respectively.

    That begs these questions:

    • Why were those block sizes chosen?

    • Why is the FreeBSD block size bigger than Linux and Mac OS X?

    • What would happen if other block sizes (e.g. 4k) were used?

    I'm just curious.

  • I'm not sure why the difference, but all that parameter does, is control how much data is read/written at a time.  You could substitute any value, and it would still work.


  • but larger block sizes give higher transfer rates, significantly reducing the time it takes to write the target disk.

  • The instructions were just gathered/added from various sources over time, indeed the block size isn't relevant aside from performance. That's the first I've noticed that actually. We'll clean that up.

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