[mythtv-users] Software RAID5 no improvement to transferspeed...

Steve Adeff adeffs at gmail.com
Thu Jan 12 18:30:04 UTC 2006

On Thursday 12 January 2006 11:47, Johnathon Meichtry wrote:
> > ----- Original Message -----
> > From: "Steve Adeff" <adeffs at gmail.com>
> > To: <mythtv-users at mythtv.org>
> > Sent: Thursday, January 12, 2006 4:21 PM
> > Subject: Re: [mythtv-users] Software RAID5 no improvement to
> > transferspeed...
> >
> > Just to let you guys know, it was an SQL issue, I sent a new email, but
> > changed the subject announcing it... I had my other machine (over 100bT)
> > running the SQL db, once I moved it back to the local machine it plays 
> > fine.
> >
> > thanks for the info though, some good info.
> >
> > Johnathon: I don't even notice 3% use by the RAID, I've seen %wa as high 
> > 6%. I get load averges around 4 while watching HD and recording 2 shows.
> >
> > Ramses: great command! I need to store that to my repertoire.
> >
> Hi Steve,
> Cool!
> On my modern 3.6GHZ server, cpu usage on raid is negligible - something
> less than 1% but on much slower machines in the past I have seen it up
> around 3% so the point I was trying to make was that it should never cause
> the CPU to head up into the 90's under even the most extreme situation
> unless of course there is some major a bug.

gotcha, well, I don't even notice it come up in top, so I'm happy =)

> My IO waits are a different matter.  If software RAID (RAID1) is in use and
> server is busy, io waits (wa) never really exceed 10% but with my hardware
> RAID5 array frequently I see it getting up to 40% io waits if it is really
> busy.  Its quite ironic as that is why I paid loads of money for it - my
> bet is there is a bug in the controller firmware but the manufacturer
> doesn't seem to be doing much about it at least the server performs well so
> I don't bother myself too much over it.

Ok, I've got only one RAID array, RAID 5, my db is currently on a non RAID 
UDMA5 ATA Seagate Barracuda 7200 drive (might move this to RAID5 for 
protection though). In top, my wa% is always at 0.0, with occasional jumps to 
3.3 or 3.4 (this is with top's update speed set to .3).
Right now I'm recording 2 HD shows and watching 1, recording 1 PBS show and 
watching 1 in fact, with 
load average: ~5.50 ~5.10 ~3.5
cpu ~90%us, 0.0% wa.
and no visible visual or audio hiccup.

Some of this is due to the xorg.conf changes I made, documented in another 
email to the list.

> If your load averages are 0.40 then to me that is fine but if it is 4.00
> then that is not so good as most Unix pros would consider that to be an
> overloaded CPU.  Of course its all speculation and people interpret load
> averages differently.

I can understand, look at what top says my load averages are, sure I'm dong a 
lot but I'm not seeing anthing wrong with my playback as I watch a PBS HD 


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