[mythtv-users] Slow video on XFS raid 0, ok video on ext3 on single drive.

[Listbox]

The RAID devices are hde and hdg, the/ partition is hdc.... to me this looks
like all my physical drives give comparable throughput.

/dev/hda:
 Timing cached reads:   1668 MB in  2.00 seconds = 834.10 MB/sec
 Timing buffered disk reads:   88 MB in  3.05 seconds =  28.87 MB/sec

/dev/hdb:
 Timing buffered disk reads:  
/dev/hdc:
 Timing cached reads:   1696 MB in  2.00 seconds = 847.36 MB/sec
 Timing buffered disk reads:   88 MB in  3.05 seconds =  28.82 MB/sec

/dev/hde:
 Timing cached reads:   1680 MB in  2.00 seconds = 838.49 MB/sec
 Timing buffered disk reads:  168 MB in  3.03 seconds =  55.46 MB/sec

/dev/hdf:
 Timing cached reads:   1688 MB in  2.00 seconds = 843.57 MB/sec
 Timing buffered disk reads:  164 MB in  3.00 seconds =  54.59 MB/sec

/dev/hdg:
 Timing cached reads:   1696 MB in  2.00 seconds = 846.68 MB/sec
 Timing buffered disk reads:  162 MB in  3.03 seconds =  53.45 MB/sec

So, given the same hardware throughput, I would expect better performance
with the XFS+RAID setup. This is not the case.
My adapter is a:
RAID bus controller: Silicon Image, Inc. PCI0680 Ultra ATA-133 Host
Controller (rev 02)
I also tried upping the PCI latency of the RAID card with 
        setpci -v -s 01:07.0 latency_timer=B0 # PCI0680 Ultra ATA-133 Host
But this had no effect. The DVB card has a latency of 32(decimal).

I just reformatted with ext3, and tried again, and got the same degradation.
It's looking like the RAID is the problem, but I do not,NOT,NOT! want to
un-stripe the disks. 

What else to try?

Listbox

-----Original Message-----
From: Andrew Lyon [mailto:andrew.lyon at gmail.com] 
Sent: Saturday, December 30, 2006 11:31 AM
To: Discussion about mythtv
Subject: Re: [mythtv-users] Slow video on XFS raid 0,ok video on ext3 on
single drive.

On 12/30/06, Listbox <listbox at hymerfania.com> wrote:
> Hi folks!
>
> I have two Seagate 160gb drives in a RAID 0 array on an SiI0680 PCI 
> ATA raid controller. I formatted an XFS filesystem on a single 
> partition, and set mythbackend to use it. My DVB card is a DviCO 
> Fusion Gold 3,( Conexant CX23880).
>
> When I watch live TV, I get terrible artifacts on digital TV, and slow 
> frame rates on analog. When I reset mythbackend to use a ext3 
> partition on a single drive, performance is acceptable.
>
> I went to considerable trouble to get the RAID and XFS working on my 
> Fedora
> 5 system, and it's pretty discouraging to see that it actually 
> degrades instead of enhances performance. What is likely the problem? 
> Is it the controller, the raid or the filesystem?
>
> Thanks for any advice!
>
> Listbox
>
> _______________________________________________
> mythtv-users mailing list
> mythtv-users at mythtv.org
> http://mythtv.org/cgi-bin/mailman/listinfo/mythtv-users
>

Please use hdparm -tT to benchmark the speed of your drives, and your raid
array, e.g.

hdparm -tT /dev/sda /dev/sdb /dev/sdc /dev/md0

You should do this when the system is idle, perhaps even in single user
mode.

That should shed some light on the situation.

Andy
_______________________________________________
mythtv-users mailing list
mythtv-users at mythtv.org
http://mythtv.org/cgi-bin/mailman/listinfo/mythtv-users