![]() ![]() With two consecutive buffers, the pipe could keep downloading and extracting for a while in the background.īut without a buffer, the whole pipe would immediately slow down at once, and would rarely ever reach full speed again. Even if it didn't, without a buffer the whole pipe is sensitive to slowdowns.įor example, when flashing directly from the internet, I found that some USB devices occasionally did a flush or something, and that causes a periodic slowdown. I'm pretty sure that a simple '>' would do it one bit at a time. What if you dont even use dd, just `wget. (and when you want to have the world's fastest img downloader, every second counts.)Īdditionally, in my script I go a couple steps further by loading the first 100MB of the img into cache first, and also it uses the buffer package to overcome I/O bottlenecks for maximum efficiency. It usually cut down on download time by around 3 seconds. In my tests, I found it gives a bit of a buffer. The cp command (which is very fast in my tests) uses just 128KB block size (see strace cp. Just for my interest, why are you using "bs=10M" for the dd command? Now I just use "cp" - its simple to use and fast enough in practice (slightly faster than dd bs=1m) I gave up trying to calculate everything and produce an optimal C program! So, given that the disk read times are near zero for this case only, whats the best read/write block size to give dd for the optimal overlap between reads and writes? įor example, I usually download the image to a memory disk, then uncompress it and copy it to the raw device. Given all the above variables, any simple benchmark results will be meaningless. Its incredibly complicated given: different read/download speeds, decompression speeds, indeterminate overlap between reads and writes, disk write speeds, variable asynchronous disk block prefetch ranges, "sync" time, verification time, etc etc Linux – umount: /filesystem: device is busy.Believe it or not, with enough optimization, it can be faster to download an img, extract it, and flash it to a SD card, than to flash a local, pre-extracted.RHEL6 – mkfs.ext4: Size of device too big to be expressed in 32 bits.HP-UX – /var is filling up and found /var/stm/logs/os. ![]()
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