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Date:      Fri, 5 Nov 2010 08:56:52 +0100 (CET)
From:      Oliver Fromme <olli@lurza.secnetix.de>
To:        freebsd-fs@FreeBSD.ORG, freebsd@jdc.parodius.com
Subject:   Re: Using an SSD "disk" for /
Message-ID:  <201011050756.oA57uqdW030090@lurza.secnetix.de>
In-Reply-To: <201011041823.oA4INTIL097844@lurza.secnetix.de>

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Oliver Fromme wrote:
 > With /usr/src and /usr/obj both on the same SATA-300 HDD,
 > a buildworld takes 10 minutes and 13 seconds.
 > 
 > With /usr/src and /usr/obj on separate memory disks,
 > a buildworld takes 10 minutes and 4 seconds.
 > 
 > This is stable/8 with empty /etc/src.conf, i.e. a complete
 > buildworld.  The machine is an AMD Phenom II X6 (hexacore).

I think I should give some more information about the
system that I used for the test.

The HDD is accessed via ahci(4) and ada(4) with NCQ.
This might make a small difference, though I haven't
benchmarked it.  src and obj are mounted with noatime.
In the memory disk case, src was even mounted read-only,
and obj was mounted async.

I made sure that there was no swapping / page-out
activity during the memory disk test, so all the data
really stayed in RAM (which should be even faster
than an SSD, I assume).  The system was otherwise idle,
gstat(8) basically showed nothing on ada0 during the
memory disk test.

The following sysctl tunings are in effect:

vfs.hirunningspace=8388608
vfs.lorunningspace=1048576
vfs.read_max=32
vfs.ufs.dirhash_maxmem=33554432
kern.sched.preempt_thresh=220

(I've got more things in /etc/sysctl.conf, but the rest
shouldn't affect file system performance or buildworld,
I think.)

The kernel is running with HZ=300 (unfortunately HZ isn't
dynamic in FreeBSD, so I'm using 300 as a trade-off).
AUDIT and MAC are disabled.

Best regards
   Oliver

-- 
Oliver Fromme, secnetix GmbH & Co. KG, Marktplatz 29, 85567 Grafing b. M.
Handelsregister: Registergericht Muenchen, HRA 74606,  Geschäftsfuehrung:
secnetix Verwaltungsgesellsch. mbH, Handelsregister: Registergericht Mün-
chen, HRB 125758,  Geschäftsführer: Maik Bachmann, Olaf Erb, Ralf Gebhart

FreeBSD-Dienstleistungen, -Produkte und mehr:  http://www.secnetix.de/bsd

"When your hammer is C++, everything begins to look like a thumb."
        -- Steve Haflich, in comp.lang.c++



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