maximum MAXBSIZE

[Gary Jennejohn]

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