[mythtv-users] Odd i/o issues

[Sam Hooker]

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Mike,

Is yours a software RAID5 array? If so, my own unexplained runaway I/O
issues from my last backend upgrade (from Fedora 6 to 9) were solved by
moving /var off the (software) RAID1 that contained the LVM volume which
housed the JFS filesystem which is home to my (SD) recordings. (*whew*)

If you are using software RAID5, I'd be curious to know if you get any
traction out of moving /var like that. I wonder if there were changes to
md since your previous kernel...


Cheers,

- -sth

sam hooker|mythtv at noiseplant.com|http://www.noiseplant.com


> Date: Tue, 13 Jan 2009 13:13:08 -0800
> From: "Michael D. O'Brien" <obrienmd at gmail.com>
> Subject: [mythtv-users] Odd i/o issues
> To: "Discussion about mythtv" <mythtv-users at mythtv.org>
> Message-ID:
> 	<2c38abbb0901131313j99aeb4ic267ea44c23e780f at mail.gmail.com>
> Content-Type: text/plain; charset="iso-8859-1"
> 
> In the last week I've upgraded my back and frontends to Ubuntu 8.10 and the
> newest myth-fixes.  Last night, I noticed that the show I was viewing was
> pausing every few seconds, rendering it nearly unwatchable.  I knew the
> backend was recording a few other shows and the frontends hadn't shown this
> behavior while the backend was idle earlier that day, so I did some looking
> around:
> 
> -top on the backend and frontend showed plently of available memory and idle
> cpu
> -it's not a network issue, the maximum usage in iftop on the frontend looked
> to be about 12mbps (out of 100) and on the backend around 30mbps (out of
> 1000), due to recording 2 shows off our hdhomerun while I was watching this
> other show.
> -on the backend, top shows iowait hovering around 20-40%, which isn't bad
> and was common while recording 3 HD shows and watching 1
> -on the backend, iostat -xk 1 shows something interesting: my raid5 array
> participants are all being used, but it seems that two of the drives hover
> around 10% usage, while one is constantly pegged at 100% usage.  Is this
> normal behavior in iostat -xk for a raid5 array?  it seems odd to me.
> 
> My backend is a C2D e6320 with 3GB of ram running Ubuntu 8.10 and the newest
> myth-fixes.  Myth records to a raid5 array of 3x750gb drives with a 1.5tb
> xfs file system on top.  It's connected to the network via 1000bT ethernet.
> 
> My frontends are AMD x2 4000+ with 1GB of ram running Ubuntu 8.10 and the
> newest myth-fixes.  They are connected to the network via 100bTX ethernet.
> 
> Thoughts?  I'm intrigued by the what seems to be strange iostat results on
> the backend...
> 
> -mike
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