Arch Linux

timm

Member

From: Wisconsin

Registered: 2004-02-25

Posts: 417

TFW, Error: Write(), mythtv recording problems

I'm running a mythtv box on Archlinux.  I have two drives.  I have recently started having problems with recordings with missing data; when you watch them they skip forward as though the recording process paused for a period of some seconds.  Sat down today to try to figure this out.

In /var/log/messages.log, I find the following:

Jan  7 14:16:05 localhost kernel: [1713625.388277] ivtv1: All encoder MPG stream buffers are full. Dropping data.
Jan  7 14:16:05 localhost kernel: [1713625.388280] ivtv1: Cause: the application is not reading fast enough.
Jan  7 14:16:05 localhost kernel: [1713625.453542] ivtv1: All encoder MPG stream buffers are full. Dropping data.
Jan  7 14:16:05 localhost kernel: [1713625.453544] ivtv1: Cause: the application is not reading fast enough.

and in mythbackend.log, I am getting:

2012-01-07 14:58:46.974 TFW, Error: Write() -- IOBOUND begin remaining(18023) free(0) size(2097152) cnt(1)
2012-01-07 14:58:50.851 TFW, Error: Write() -- IOBOUND end
2012-01-07 14:59:34.793 TFW, Error: Write() -- IOBOUND begin remaining(5697) free(0) size(2097152) cnt(1)
2012-01-07 14:59:37.976 TFW, Error: Write() -- IOBOUND end

I found some info that suggested that I have hit the I/O limits of my drives.  It suggested that I run iostat -xk 2 (part of the sysstat package in Arch), and I am getting nearly 100% utilization of both drives for periods when recording.

I deleted some files to create some space, and noticed (running iostat in a terminal window) very high utilization on the drives for this operation.  Not sure what's normal in this regard.

My drives are set up with the system on sda and then a btrfs system spanning from sda across sdb for recordings. 

My fstab is:

# <file system> <dir>   <type>  <options>       <dump>  <pass>
tmpfs           /tmp    tmpfs   nodev,nosuid    0       0
/dev/sda7 /srv/mythtv btrfs defaults 0 1
LABEL=boot /boot ext2 defaults 0 1
LABEL=home /home ext4 defaults 0 1
LABEL=root / ext4 defaults 0 1
LABEL=swap swap swap defaults 0 0
LABEL=var /var ext3 defaults 0 1

When I first built the machine, we weren't having any problems.  At this point, the recording filesystem is essentially full, with mythtv deleting programs as needed for space.  As noted above, I'm manually deleting some files to see if this is part of the problem.

One site suggested moving /var to a different drive to help solve this problem, haven't figured out what to do with that yet.

At this point I'm still experimenting, but wanted to get this out here for ideas, or hopefully for those who come next when I solve it......

Update:
I cleared significant drive space through deletions; this has not fixed the issue.

Last edited by timm (2012-01-14 02:56:41)