maximum MAXBSIZE

[Wojciech Puchar]

why FreeBSD default is so completely wrong for modern hardware?

i think 4MB is OK for HDDs, more may be optimal for RAID5 arrays.


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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