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Re: Could RAM possibly be just 3-4 times faster than bare hdd writes and reads? or, is the Linux kernel doing its 'magic' in the bg? or, ...

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	Hi.

On Wed, Jun 17, 2020 at 12:10:51PM -0700, David Christensen wrote:
> 2.  AIUI dd(1) uses asynchronous (buffered) I/O unless told otherwise.

You seem to confuse asynchronous and cached I/O too.

>From Linux kernel POV, *asynchronous* I/O is a pair of
io_submit/io_getevents syscalls, and dd does not do these regardless of
the options that are provided.
What dd does is a *synchronous* I/O (read/write syscalls or
pread64/pwrite64 for older kernels).

Whenever the I/O is cached (an output file is opened without
O_DIRECT|O_DSYNC flags) or not is orthogonal to whenever it's sync or
async. 

For the true async I/O you'll need something like fio, not dd.

Reco

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Could RAM possibly be just 3-4 times faster than bare hdd writes and  reads? or, is the Linux kernel doing its 'magic' in the bg? or, ... Albretch Mueller <lbrtchx@gmail.com> - 2020-06-17 12:20 +0200
  Re: Could RAM possibly be just 3-4 times faster than bare hdd writes  and reads? or, is the Linux kernel doing its 'magic' in the bg? or, ... Albretch Mueller <lbrtchx@gmail.com> - 2020-06-17 12:20 +0200
    Re: Could RAM possibly be just 3-4 times faster than bare hdd writes  and reads? or, is the Linux kernel doing its 'magic' in the bg? or, ... Dan Ritter <dsr@randomstring.org> - 2020-06-17 16:10 +0200
    Re: Could RAM possibly be just 3-4 times faster than bare hdd writes  and reads? or, is the Linux kernel doing its 'magic' in the bg? or, ... Andy Smith <andy@strugglers.net> - 2020-06-18 01:00 +0200
  Re: Could RAM possibly be just 3-4 times faster than bare hdd ... "Thomas Schmitt" <scdbackup@gmx.net> - 2020-06-17 12:50 +0200
  Re: Could RAM possibly be just 3-4 times faster than bare hdd          writes and reads? or, is the Linux kernel doing its          'magic' in the bg? or, ... Linux-Fan <Ma_Sys.ma@web.de> - 2020-06-17 13:30 +0200
  Re: Could RAM possibly be just 3-4 times faster than bare hdd writes  and reads? or, is the Linux kernel doing its 'magic' in the bg? or, ... Michael Stone <mstone@debian.org> - 2020-06-17 14:00 +0200
  Re: Could RAM possibly be just 3-4 times faster than bare hdd writes  and reads? or, is the Linux kernel doing its 'magic' in the bg? or, ... Dan Ritter <dsr@randomstring.org> - 2020-06-17 15:50 +0200
  Re: Could RAM possibly be just 3-4 times faster than bare hdd writes  and reads? or, is the Linux kernel doing its 'magic' in the bg? or, ... Anders Andersson <pipatron@gmail.com> - 2020-06-17 16:10 +0200
    Re: Could RAM possibly be just 3-4 times faster than bare hdd writes  and reads? or, is the Linux kernel doing its 'magic' in the bg? or, ... Albretch Mueller <lbrtchx@gmail.com> - 2020-06-17 17:50 +0200
  Re: Could RAM possibly be just 3-4 times faster than bare hdd writes  and reads? or, is the Linux kernel doing its 'magic' in the bg? or, ... David Christensen <dpchrist@holgerdanske.com> - 2020-06-17 21:20 +0200
    Re: Could RAM possibly be just 3-4 times faster than bare hdd writes  and reads? or, is the Linux kernel doing its 'magic' in the bg? or, ... Reco <recoverym4n@enotuniq.net> - 2020-06-17 21:30 +0200
      Re: Could RAM possibly be just 3-4 times faster than bare hdd writes  and reads? or, is the Linux kernel doing its 'magic' in the bg? or, ... David Christensen <dpchrist@holgerdanske.com> - 2020-06-17 22:30 +0200
        Re: Could RAM possibly be just 3-4 times faster than bare hdd writes  and reads? or, is the Linux kernel doing its 'magic' in the bg? or, ... <tomas@tuxteam.de> - 2020-06-17 22:40 +0200
          Re: Could RAM possibly be just 3-4 times faster than bare hdd writes  and reads? or, is the Linux kernel doing its 'magic' in the bg? or, ... Reco <recoverym4n@enotuniq.net> - 2020-06-17 22:50 +0200
            Re: Could RAM possibly be just 3-4 times faster than bare hdd writes  and reads? or, is the Linux kernel doing its 'magic' in the bg? or, ... <tomas@tuxteam.de> - 2020-06-17 23:10 +0200
              Re: Could RAM possibly be just 3-4 times faster than bare hdd writes  and reads? or, is the Linux kernel doing its 'magic' in the bg? or, ... Reco <recoverym4n@enotuniq.net> - 2020-06-17 23:10 +0200
            Re: Could RAM possibly be just 3-4 times faster than bare hdd writes  and reads? or, is the Linux kernel doing its 'magic' in the bg? or, ... Michael Stone <mstone@debian.org> - 2020-06-18 00:00 +0200
              Re: Could RAM possibly be just 3-4 times faster than bare hdd writes  and reads? or, is the Linux kernel doing its 'magic' in the bg? or, ... Reco <recoverym4n@enotuniq.net> - 2020-06-18 08:00 +0200
                Re: Could RAM possibly be just 3-4 times faster than bare hdd writes  and reads? or, is the Linux kernel doing its 'magic' in the bg? or, ... Michael Stone <mstone@debian.org> - 2020-06-18 15:00 +0200
                Re: Could RAM possibly be just 3-4 times faster than bare hdd writes  and reads? or, is the Linux kernel doing its 'magic' in the bg? or, ... Reco <recoverym4n@enotuniq.net> - 2020-06-18 16:30 +0200
                Re: Could RAM possibly be just 3-4 times faster than bare hdd writes  and reads? or, is the Linux kernel doing its 'magic' in the bg? or, ... Michael Stone <mstone@debian.org> - 2020-06-18 18:00 +0200
        Re: Could RAM possibly be just 3-4 times faster than bare hdd writes  and reads? or, is the Linux kernel doing its 'magic' in the bg? or, ... Reco <recoverym4n@enotuniq.net> - 2020-06-17 23:10 +0200

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