[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

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



-------------- next part --------------
An HTML attachment was scrubbed...
URL: http://mythtv.org/pipermail/mythtv-users/attachments/20060321/87fc3586/attachment.htm 


More information about the mythtv-users mailing list