Changing bs=1m to bs=16m gives absolutely no difference in reading speed. Then I decided to test reading speed: 26MB/s for /dev/disk vs 87MB/s for /dev/rdisk. Changing bs=1m to bs=16m gives absolutely no difference in writing speed. Repeated tests several times, but results were stable: 17MB/s for /dev/disk vs 20MB/s for /dev/rdisk. Just wrote 2GB disk image to Sandisk Ultra MicroSD 64GB ( ). It seems /dev/disk and /dev/rdisk works different for HDDs and SSDs. It does not do any read ahead or write behind. It does small (4KB/16KB) I/Os, which leads to a lot of per-I/O overhead. It caches even if not strictly necessary like if the device could memory map and directly transfer into your app's buffer. The caching being done by /dev/disk’s read and write paths is very simple and almost brain dead. When streaming, like via dd, 128KB to 1MB are pretty good sizes to get near-optimal performance on current non-RAID hardware. The lower layers may break it up (eg., USB breaks it up into 128KB pieces due to the maximum payload size in the USB protocol), but you generally can get bigger and more efficient I/Os. If you do a read or write larger than one sector to /dev/rdisk, that request will be passed straight through. In contrast, /dev/rdisk basically just passes the read or write straight to the device, which means the start and end of the I/O need to be aligned on sector boundaries. This is nice in that you can do unaligned reads and writes, and it just works. The read/write path for /dev/disk breaks up the I/O into PAGE_SIZE chunks (4KB on x86 and arm, 16KB on arm64), which it reads into the buffer cache, and then copies into the user space buffer (and then issues the next chunk-sized read…). One of the key differences between /dev/disk and /dev/rdisk, when you access them from user space, is that /dev/disk is buffered. Thank you in advance.The accepted answer is right, but it doesn’t go into much detail. Would be great to have some feedback from you. Changed 12.6.06 to 12.6.03 in ist -file, using the following command: sudo plutil -replace CFBundleShortVersionString -string "12.6.03" /Applications/Install\ macOS\ Sierra.app/Contents/istĮven with these changes I still didn’t manage to make it work.Change the name of the flash drive to “Untitled” or “untitled” (also changed the volume name in the command).Unfortunately, after using this command I‘ve encountered the message “/Volumes/MyVolume is not a valid volume mount point”… I made some search, and tried these steps, to solve the problem: Used the following command in Terminal to create the bootable macOS Sierra USB installer: sudo /Applications/Install\ macOS\ Sierra.app/Contents/Resources/createinstallmedia -volume /Volumes/MyVolume -applicationpath /Applications/Install\ macOS\ Sierra.app.Connected an USB flash drive Extended (Journaled) of 16gb of empty space, with the name “MyVolume”.Downloaded the macOS Sierra, from the apple website.Hello everyone, I’m trying to create a bootable USB installer for macOS Sierra for my iMac mid 2010.
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