[mythtv-users] Source of my IOBOUND problem?

[Craig Huff]

Date: Thu, 7 Jun 2007 17:10:29 -0700
From: Blammo <blammo.doh at gmail.com>
Subject: Re: [mythtv-users] Source of my IOBOUND problem?

> On 6/6/07, Craig Huff <huffcs at yahoo.com> wrote:
> > I had been under the impression (apparently wrong) that three (3) SD recording streams
> > would not approach the available bandwidth of a standard (reasonably current) PATA disk.
> > Did I choose a clunker drive?
> >
> > How do you tell (from all that data) that this is the problem (not to argue, but for education)?
> 
> Couple other things you might check:
> 
> IO Scheduler: I've had really good luck with the "deadline" scheduler,
> when it comes to real time applications and heavy disk usage.
> Commercial flaggers can pound your disk IO, and the deadline scheduler
> seems to make them all play in nice(r) time slices
> 
> Thrashing: Consider moving MySQL to a different physical disk.
> Especially during things like commercial flagging, the writes can be
> rapid and frequent.
> 
> Disk Performance: Your HD may be rated for 100M a second, but that's
> sequential reads on the best part of the disk. Throwing in 2,3 or 4
> more reads/writes to different parts of the disk does way more than
> half or quarter that number. Consider additional disks, or some form
> of raid/striping.
> 
> Commercial Flagging: Consider restricting the time you flag to times
> you don't record.. IE midnight to 6am or something.
> 
> the problem you're experiecing is fixable, we've all been there at one
> phase or another in our myth growth..


Boy,  having been a Solaris sysadmin for many years just doesn't help when 
dealing with Linux.  -- so many things I never had to deal with --

I am running FC6, FWIW, so I have been running on the theory of "Plug and 
Play" software. As a result, I'll need more information on some of your 
suggestions before I can pursue them.

IO Scheduler:  How do I determine what I've got running, how do I find what 
    alternatives I already have available, how do I switch to one of those, and how 
    do I go about getting the "deadline" scheduler if I don't already have it as part 
    of my FC6 installation?

Thrashing and Disk Performance:  Doable, and have this plan in mind:
    Install second disk to put all but /video partition on,
    mount equivalent partitions under /mnt and run
            # dump /current/hda# | restore /new/hdb#
    until all migrating partitions are copied, edit /etc/fstab (keeping a copy of the 
    original!), and reboot (with my trusty Knoppix LiveDVD at the ready ;-)

    If this fails, then it's on to software RAID striping SATA disks -- this is a good
    excuse for expanding storage capacity AND dipping my toes in the SATA pool
    for the first time, eh?

    Also, I get the feeling I should be adding more RAM.  Currently I have 512MB.
    Recommendations, anyone?

Commercial Flagging:  Ummm...How?
    I know how to schedule jobs with cron and anacron, but how do I restrict what 
    times mythcommflag CAN run?


Thanks for the advice and encouragement.

Craig.




       
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