maximum MAXBSIZE

[Warner Losh]

Netflix runs our entire network at MAXPHYS=8MB since we're doing huge reads
off HDD.

Warner


On Thu, Jan 9, 2020 at 2:58 AM Wojciech Puchar <wojtek at puchar.net> wrote:

> 2MB MAXPHYS was what i have set for over 3 years without problems.
>
> On Wed, 8 Jan 2020, Conrad Meyer wrote:
>
> > Bufs are dynamically allocated from uma now, and perhaps a middle ground
> BSIZE is worth considering? Would 1MB and 2kB bufs (1kB
> > 32-bit) be awful?
> >
> > Cheers,
> > Conrad
> >
> > On Wed, Jan 8, 2020 at 06:18 Konstantin Belousov <kostikbel at gmail.com>
> wrote:
> >       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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