maximum MAXBSIZE

[Konstantin Belousov]

On Wed, Jan 08, 2020 at 02:52:57PM +0100, Wojciech Puchar wrote:
> sorry i made a mistake - i change MAXPHYS not MAXBSIZE.
> 
> 16MB works for now without problems
MAXPHYS 16MB means that sizeof(struct buf) is around 32K (16K on 32bit).

> 
> On Wed, 8 Jan 2020, Gary Jennejohn wrote:
> 
> > On Tue, 7 Jan 2020 22:47:54 +0000
> > Rick Macklem <rmacklem at uoguelph.ca> wrote:
> > 
> > > Hans Petter Selasky wrote:
> > > > On 2020-01-07 22:12, Wojciech Puchar wrote:
> > > > > default MAXBSIZE is 128kB. badly low for todays magnetic disks.
> > > > > 
> > > > > i have it set to 2MB on all computers that have magnetic disks. Great
> > > > > improvement with large files. especially when more than one are
> > > > > read/wrote in parallel. And no problems experienced
> > > > > 
> > > > > But for optimal performance MAXBSIZE should be transfered in few times
> > > > > longer than average seek time. todays disk do 200-250MB/s so 2MB is
> > > > > transfered below 10ms.
> > > > > 
> > > > > 8-16MB seems like good choice. is there any reason not to set it that high?
> > > > 
> > > > Old disk may not support it, especially USB 1.0/2.0 disks.
> > > I also thought it was limited to MAXPHYS, but maybe I'm only thinking of the NFS
> > > specific case?
> > > 
> > 
> > There's a comment in param.h that it should not exceed MAXPHYS to be
> > on the safe side.  How old that comment is I can't say and that may
> > not be the case today.
> > 
> > MAXBSIZE is only 64KiB in my param.h.
> > 
> > I have to agree with HPS.  There are many old bridge-chips still in
> > use and problems with a large MAXBSIZE might occur.  It's certainly
> > not uncommon to see capacity limitations - I have a docking station
> > which can't see more than 3TB.
> > 
> > -- 
> > Gary Jennejohn
> > 
> > 
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