freebsd stable - Jul 2012 - 8.2 ->8.3 regression on disk writes

Hello,

using 8.2 the machine runs fine,
using 8.3 or higher, not so much.

In laymans terms,
if I do "too many" writes/time just once, the machine can't do any
disk
access for a couple of hours.

As in: What's already running stays running, no crashes or anything,
but as soon as I need to read from disk (login, start program not cached  
in memory from previous run),
I'm all out of luck.
I killed the testing ftp-transfer about 15 seconds after the transfer  
speed dropped,
now I'm waiting for 10+ minutes for ``top'' to start.


I can install ports and kernels and world fine,
but "ezjail-admin install" or transferring a few GB of files from
another
machine sends it to limbo.

The next step would likely be to go through the kernel changes between 8.2  
and 8.3 to narrow it down,
I'd appreciate pointers as to what kernel changes to look out for,
or other suggestions on what to do.

Verbose dmesg: http://gurder.ross.cx/misc/dmesg.txt

TIA,

Michael


Postscript: That's the same problem I wrote about in "Trouble with
gmirror
and device ada",
turns out using gmirror just makes the problem appear much faster as  
opposed to eventually.

----- Original Message ----- 
From: "Michael Ross" <gmx@ross.cx>
To: <freebsd-stable@freebsd.org>
Sent: Monday, July 16, 2012 2:23 PM
Subject: 8.2 ->8.3 regression on disk writes

> Hello,
> 
> using 8.2 the machine runs fine,
> using 8.3 or higher, not so much.
> 
> In laymans terms,
> if I do "too many" writes/time just once, the machine can't
do any disk
> access for a couple of hours.
> 
> As in: What's already running stays running, no crashes or anything,
> but as soon as I need to read from disk (login, start program not cached  
> in memory from previous run),
> I'm all out of luck.
> I killed the testing ftp-transfer about 15 seconds after the transfer  
> speed dropped,
> now I'm waiting for 10+ minutes for ``top'' to start.
> 
> 
> I can install ports and kernels and world fine,
> but "ezjail-admin install" or transferring a few GB of files from
another
> machine sends it to limbo.
> 
> The next step would likely be to go through the kernel changes between 8.2
> and 8.3 to narrow it down,
> I'd appreciate pointers as to what kernel changes to look out for,
> or other suggestions on what to do.
> 
> Verbose dmesg: http://gurder.ross.cx/misc/dmesg.txt
You have some strangeness there:

I see:

"real memory  = 17179869184 (16384 MB)"
"avail memory = 2050920448 (1955 MB)"

So even though you have 16GB ram your only using 2GB of it which
will likely cause slowness under ZFS including disabling prefetch

"ZFS NOTICE: Prefetch is disabled by default if less than 4GB of
RAM is present; to enable, add "vfs.zfs.prefetch_disable=0" to
/boot/loader.conf."

Is this a VM or something?

    Regards
    Steve


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Have you tried switching your scheduler to 4BSD?

-- 

    Change is hard.

Am 17.07.2012, 06:06 Uhr, schrieb Doug Barton <dougb@freebsd.org>:
> Have you tried switching your scheduler to 4BSD?
>
Just out of interest I tried, no change.

Thanks,

Michael