On Mon, Sep 17, 2001 at 12:34:23AM -0700, Matthew Jacob wrote:
> > 
> > 1) The clock slippage *may* be limited to the end of the backup runs; I
> >    can't shake the feeling that I've seen it otherwise, but... it may
> >    only happen when I do the close(); however, it does happen with either
> >    the rewinding or non-rewinding device.
> 
> The filemark writes can take a long time- all data in a write buffer will
> flush. But this shouldn't cause any lossage.
> 
> I don't recall what HBA this is... let me go back and look at old mail...you
> said "various machines"- did they all have the same HBA type (Advansys)?

No; the machine with the DLT2000XT in it has a Qlogic 1280.

> Looking again at #2 above- this makes me wonder if this isn't some scheduler
> problem, oddly enough. It sounds to me like the backup process runs and
> consumes a very large quantum of runtime because it's being so succesful at
> pushing data- so much so that when it has to wait a bit (because the internal
> tape buffer is full and needs to flush a bit), that it gets penalized and
> doesn't get started quickly enough when the command that waited on a tape
> buffer flush finishes. But this may make no sense at all.

I wondered about *exactly* this, so I tried raising HZ on my machines to
make the scheduler quantum smaller.  Throughput increased very slightly,
but I still couldn't stream -- and I lost much more time, too.

-- 
Thor Lancelot Simon	                                      tls@rek.tjls.com
    And now he couldn't remember when this passion had flown, leaving him so
  foolish and bewildered and astray: can any man?
						   William Styron