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RE: /proc/sys/vm/bdflush



These are my current settings for bdflush:

40 10 0 0 60 512 60 0 0

according to the advice at the following URL:

http://www-106.ibm.com/developerworks/linux/library/l-fs8/

The article recommends a 300 where the 512 is above, but looking at the
kernel source it seems the Red Hat kernel limits the low end of this
parameter to be 512.

As the article states "it's slightly less efficient to do things this
way since the kernel will have fewer opportunities to combine writes,"
but with the above parameters I have good interactive performance from a
data=ordered ext3 RAID volume with 400 users and load averages of 10+ on
a quad Xeon 1.4GHz with 8GB RAM.

I have a question as well - according to tests performed for the article
above, "ext3's data=journal mode is incredibly well-suited to situations
where data needs to be read from and written to disk at the same time."
This is the situation that exists on my box.  

My question is: has anyone had any real-world experience to backup the
claims of the above statement?  I would love to get better performance,
AND have better data integrity, but that seems to good to be true :)

Thanks,
Andy.


-----Original Message-----
From: Ralf Hildebrandt [mailto:Ralf Hildebrandt charite de] 
Sent: Thursday, November 21, 2002 6:00 AM
To: Ext3 Users
Cc: Udo Wolter
Subject: Re: /proc/sys/vm/bdflush


* Marc-Christian Petersen <m c p gmx net>:

> > Linux postamt1.charite.de 2.4.19-ac4 #1 Mon Aug 19 14:35:20 CEST
2002 i686

> There is your problem. 2.4.19 and even latest 2.4.20 has those kind of

> behaviour in some situations. I had the same experience. Read the
thread 
> between Andrea and me some days ago.
> 
> Someone wrote you can use:
> 
> elvtune -r 2048 -w 131072 /dev/$yourdevice
> echo "90 500 0 0 600000 600000 95 20 0" >/proc/sys/vm/bdflush
> 
> and with those settings the "freeze" behaviour is gone but I cannot
confirm 
> that. 2.4.19|2.4.20 has those problems too even with those settings,
but not 
> as worst as without it.

We shall try that. Right now I'm running 2.4.20-rc2, but still have
the occasional lockup.

-- 
Ralf Hildebrandt (Im Auftrag des Referat V a)
Ralf Hildebrandt charite de
Charite Campus Mitte                            Tel.  +49 (0)30-450
570-155
Referat V a - Kommunikationsnetze -             Fax.  +49 (0)30-450
570-916



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