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RE: On very different journalling activity on 2 servers.



Thank you Stephen,

We will do a kernel upgrade as you suggest & then see what is what.

We'll do it early tomorrow morning & will let you most helpful people know
what happened.

Thanks again - great suppport.

Regards,
Nico Morrison
nico morrison micronicos com
___________________________________________
Micronicos Limited  -  London, UK.
Tel: +44 20 8870 8849 Fax: +44 20 8870 5290
___________________________________________

From: Stephen C. Tweedie [mailto:sct redhat com]
Sent: 05 February 2003 10:13
To: Nico Morrison
Cc: 'Andrew Morton'; ext3 users list
Subject: RE: On very different journalling activity on 2 servers.


Hi,

On Wed, 2003-02-05 at 08:45, Nico Morrison wrote:

> [root ns5 nico]# /sbin/hdparm  /dev/hda
> /dev/hda:
>  using_dma    =  0 (off)

> Does this mean that dma is in fact off?

Yes.

> Looks like is ON on the server that has no problems and OFF on the one
with
> loadsa journalling?

Yes.

> What do we need to do & is it safe to turn DMA ON on a busy working public
> internet server?

You don't.  

The trouble is, the kernel usually has a reason for not being in DMA
mode.  If it can negotiate DMA, it will; but the older of your two
systems did not do so, so either that older kernel doesn't know how to
drive the IDE controller in DMA mode safely, or it has detected an error
on the IDE bus and has backed off to non-DMA mode automatically.  In
both cases, forcing DMA on manually is not recommended.

I'd suggest that you upgrade the 7.2 box to the current errata kernel,
which is the same across all the 7.* releases.  That should give you the
same updated IDE drivers as the 7.3 box has, and will hopefully get you
running DMA properly.  If it doesn't, then you're going to have to check
the logs to see why DMA isn't being negotiated.

Cheers,
 Stephen





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