maximum MAXBSIZE

[Warner Losh]

On Thu, Jan 9, 2020 at 8:45 AM Gary Jennejohn <gljennjohn at gmail.com> wrote:

> On Thu, 9 Jan 2020 15:21:25 +0100 (CET)
> Wojciech Puchar <wojtek at puchar.net> wrote:
>
> > why FreeBSD default is so completely wrong for modern hardware?
> >
> > i think 4MB is OK for HDDs, more may be optimal for RAID5 arrays.
> >
>
> POLA (principle of least amazement).  I certainly don't need a MAXPHYS set
> to 4MB on my desktop machine.  Not everyone using FreeBSD is running
> servers with large amounts of memory and disk storage.
>
> It's a trivial change if it's beneficial in a certain use scenario.  The
> decision should be left up to the user.
>

And if you change MAXPHYS, you'll also want to bump the insanely small
runningbuf limits. And there may be a few other parameters I've not
reported that we set that are critical too :)

Warner


> >
> > On Thu, 9 Jan 2020, Warner Losh wrote:
> >
> > > 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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> --
> Gary Jennejohn
>