[CentOS] slow system

Ross S. W. Walker

rwalker at medallion.com
Sat Jan 13 05:53:25 UTC 2007


> -----Original Message-----
> From: centos-bounces at centos.org 
> [mailto:centos-bounces at centos.org] On Behalf Of Craig White
> Sent: Saturday, January 13, 2007 12:40 AM
> To: CentOS mailing list
> Subject: Re: [CentOS] slow system
> 
> On Fri, 2007-01-12 at 23:16 -0600, Les Mikesell wrote:
> > Craig White wrote:
> > >>> I have software RAID level 1 and the mirrored drives 
> are the master &
> > >>> slave on the primary controller and I'm thinking that 
> is my mistake.
> > >>>
> > >>> Is there a simple method for changing the configuration 
> of md before I
> > >>> switch the slave drive to be the slave on the secondary 
> controller?
> > >>>
> > >> I think they will pair up automatically if you shut down cleanly
> > >> and move the connector.  If not, just 'mdadm --add' it back after
> > >> it comes up with a missing member.  If you have to add it back,
> > >> the drives will have to resync so there is a small risk of
> > >> failure during the process.
> > > ----
> > > great thanks - am I right in thinking that having both 
> mirrored drives
> > > on the same controller master/slave is likely a cause of slowness?
> > 
> > It will make some difference on writes, but reads should only
> > be done on one of the drives anyway.  I doubt if it makes a huge
> > difference unless you have an application writing all the time.
> ----
> here's my problem - system was ok and mother board died. 
> Purchased a new
> motherboard and this is what I get...
> 
> # hdparm -t /dev/md1
> 
> /dev/md1:
>  Timing buffered disk reads:    4 MB in  3.68 seconds =   1.09 MB/sec
> 
> which is dreadfully slow

Something is definitely not right here. I have an old Dell Dimension
(1GHz, 512MB) at home here that I have FC5 on, the drives are on the
first channel master/slave mirrored, cheapo 100GB WDs. Here is what I
get:

[root at gandalf linux]# hdparm -t /dev/md1

/dev/md1:
 Timing buffered disk reads:   72 MB in  3.00 seconds =  23.96 MB/sec

Now that is what I call slow, what you are getting is unusable.

I'd put then on separate channels, but I have an LS-120 drive in PIO,
and a CDRW running at like DMA2, and it would be a lot worse to share a
channel with one of those.

-Ross

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