On Fri, 2020-11-13 at 14:36 -0800, L A Walsh wrote: > On 2020/11/12 00:48, Michael J. Baars wrote: > > Hi, > > > > I needed to zero out my hard drive because one of my nodes has become > > unstable. To this purpose I used coreutils dd with the following command > > line > > arguments > > > > dd if=/dev/zero of=/dev/mmc... status=progress > > > > and I noticed how slow this program is in doing the job. So I tried a > > couple of different settings, like > > > > bs=1048576 oflag=direct > > > > but without significant improvement. The results are always the same... > > around 25 mb/s. > > > > Then I remembered this little benchmark I write not so long ago, please do > > have a look at it, it won't destroy your drive. I included the results > > obtained > > by running the benchmark on the computer I'm currently working on, so you > > can compare them to your own. > > > --- > Your benchmark uses 'random' as input, which I seem to remember having > it's own slowness. > > Using '/dev/zero' as input, I immediately got 49MB/s.
I get 83.2 mb/s using /dev/zero. The actual input to the benchmark is neither /dev/zero or /dev/random, it's ./ftesti :) Trying to achieve the same with dd: dd if=./ftesti of=./ftesto bs=1048576 count=64 oflag=direct status=progress gives a speed of 88.0 mb/s. As you can see from the log, with given blocksize, my benchmark does this exact same thing at a rate of 5663.7168 mb/s and at a maximum rate of 16589.7124 mb/s with blocksize 67108864 (the entire file at once). Why, I ask you, is dd that much slower? What is it 'actually' doing with all the processing power available? > Ensuring the file was in 1 contiguous area on disk (used xfs_fsr) and > "nfrags" > I got up to 56.1MB/s. > > Using a bs of 16MB and 4 blocks, I got up toe 64.3MB/s. > > Trying it on my larger RAID disk w/same sizes: 1.6MB/s. > > > > > Hope that one of you feels inspired enough you to pick up the dd source > > codes and finish the job. > > > --- > Is that what you meant? > > All of those are rotating rust...the 1st disk is a > RAID5. The larger Disk is a RAID10 with 6 stripes. > >
