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

Andrew Lyon andrew.lyon at gmail.com
Sun Dec 31 12:06:25 UTC 2006


On 12/31/06, Listbox <listbox at hymerfania.com> wrote:
> 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
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>
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>

You can run hdparm -tT on the raid itself, hdparm -tT /dev/md0, it
would be interesting to see what speeds that returns.

What is the master/slave arrangement of the drives? Perhaps other
devices (hdf) on the same ide bus are slowing down the raided hds.

Andy


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