[mythtv-users] 'wa' field in 'top' is +90% when recording a show
cromworshipper-mythtvlist at yahoo.com
cromworshipper-mythtvlist at yahoo.com
Tue Mar 21 22:13:27 UTC 2006
Examine the drives with smartctl:
# smartctl -a /dev/hda
or, if you're using SATA drives
# smartctl -d ata -a /dev/sda
If you're getting warning messages, take out that drive.
http://smartmontools.sourceforge.net/
John
----- Original Message ----
From: Daniel Walton <dwalton at cisco.com>
To: Discussion about mythtv <mythtv-users at mythtv.org>
Sent: Tuesday, March 21, 2006 2:07:22 PM
Subject: Re: [mythtv-users] 'wa' field in 'top' is +90% when recording a show
On Mon, 20 Mar 2006, Brian Wood wrote:
>
> On Mar 20, 2006, at 11:25 AM, Daniel Walton wrote:
>
> > I've noticed that sometimes when I'm recording tv and when watching certain
> > shows I've recorded, the cpu is pegged at 99% or 100% with most of the
> > utilization in 'wa' (wa stands for "I/O wait state"). I record a lot of HD
> > content so I have two 250 gig drives and I use LVM to make the two drives
> > appear as one to mythtv. One of these two drives is a refurb (didn't
> > realize it until after I bought it) and I suspect that I'm only seeing the
> > high wa utilization when I'm accessing the refurb drive.
> >
> > How can I verify which drive a show is stored on in a LVM enviroment? Any
> > other ideas on what could be causing wa to go sky high? Trying to playback
> > a show with the CPU hammered like this doesn't work very well.
> >
>
> I don't know what makes you so quick to blame the refurb drive, I
> don't think there's any particular reason it should be any more prone
> to trouble than a new one. The only drive I have ever had die on me
> was new, and I use a lot of refurbed drives.
I didn't have this problem before I added the refurb drive. Odds are its either
the drive or the fact that I'm using LVM. I just need a way to verify which is
the issue.
>
> I've read that LVM has a lot of overhead, more than it has any right
> to have. I have a pair of 250GB drives running as a software RAID0
> array and they work just fine, I had a lot of problems when I tried
> LVM, although I am using the system for just SD.
If the LVM overhead is what is causing my high wa cpu usage then I don't see how
LVM ever gained any popularity. Here is a good example of the problem, this is
happening when I run mythtranscode on a SD show:
backend:~# dstat -a
----total-cpu-usage---- -disk/total -net/total- ---paging-- ---system-- ---load-avg---
usr sys idl wai hiq siq|_read write|_recv _send|__in_ _out_|_int_ _csw_|_1m_ _5m_ 15m_
14 2 72 12 0 0| 0 0 | 0 0 | 0 0 | 0 0 |2.41 2.36 1.42
3 1 0 96 0 0|4740k 0 | 192B 2468B| 0 0 | 367 250 |2.41 2.36 1.42
1 1 0 98 0 0|3048k 0 | 64B 362B| 0 0 | 351 149 |2.41 2.36 1.42
0 0 0 100 0 0| 0 4096B| 64B 362B| 0 0 | 329 51 |2.38 2.35 1.42
0 0 0 97 0 3| 0 96k| 64B 346B| 0 0 | 331 52 |2.38 2.35 1.42
4 1 0 95 0 0|4100k 4096B| 64B 346B| 0 0 | 360 195 |2.38 2.35 1.42
4 2 0 94 0 0|6560k 0 | 64B 362B| 0 0 | 383 274 |2.38 2.35 1.42
5 1 0 93 1 0|8200k 0 | 64B 362B| 0 0 | 394 326 |2.38 2.35 1.42
4 2 0 94 0 0|6152k 4096B| 64B 362B| 0 0 | 377 267 |2.35 2.34 1.42
0 0 0 100 0 0| 0 0 | 64B 362B| 0 0 | 328 49 |2.35 2.34 1.42
0 0 0 100 0 0| 128k 20k| 64B 346B| 0 0 | 333 57 |2.35 2.34 1.42
1 0 0 99 0 0| 256k 0 | 64B 346B| 0 0 | 330 59 |2.35 2.34 1.42
6 4 0 90 0 0|10.4M 0 | 64B 346B| 0 0 | 413 403 |2.35 2.34 1.42
5 1 0 93 1 0|13.0M 16k| 128B 850B| 0 0 | 600 566 |2.32 2.34 1.42
10 6 0 85 0 0|7812k 0 | 128B 954B| 0 0 | 234 324 |2.32 2.34 1.42
1 0 0 99 0 0| 644k 0 | 234B 898B| 0 0 | 339 129 |2.32 2.34 1.42
^^^^^
My cpu has been pegged due to wa for 10 minutes now.
> I'm not sure how to discover which drive of an LVM array your file is stored
> on, but I believe it will use all of the capacity of the "first" drive before
> it stores anything on the second, so if this is a fairly new system it would
> be reasonable to assume your second drive is not yet being used if the total
> is less than 250GB.
I added the second drive in time for the winter olympics so I have more that
250G of recorded content.
Thanks
Daniel
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