On Thu, 2019-06-20 at 04:54 +0300, Dmitry V. Levin wrote: > On Thu, Jun 20, 2019 at 01:10:53AM +0200, Mark Wielaard wrote: > > +# Make sure the disk is reasonably fast, should be able to write > > 100MB/s > > +fast_disk=1 > > +timeout -s9 10s dd conv=fsync if=/dev/urandom of=tempfile bs=1M > > count=1K \ > > + || fast_disk=0; rm tempfile > > Why /dev/urandom? I suggest to use /dev/zero instead.
Good question. In early testing I noticed some file systems seemed to optimize away the whole writing of zeros and dd would finish almost immediately. So I used /dev/urandom to get some "real bits" in the file. But even that didn't always show the true write-through speed. Then I added conv=fsync which makes sure to physically write output file data before finishing. That seems to work to see the actual write speed with either /dev/urandom or /dev/zero. So, I'll change it to /dev/zero again. Thanks. > Also, the check itself is quite expensive, it writes 1G into > tempfile, > I suggest to move it after mem_available check. OK. Moved. > > +if test $fast_disk -eq 0; then > > + echo "Disk not fast enough, need at least 100MB/s" > > It isn't necessarily a disk, I'd say that file system is not fast > enough. Changed. Thanks, Mark
