[vdr] Re: Broken recordings (many mpeg errors and artifacts)

[Mans Krancher <bobdylan23@web.de>]

> > > Could someone find an explanation for this really strange symptom?
> > 
> > Now the vdr is crashing every 1-2 min., but only during recordings and
> > only at Pro7 & Co. The /var/log/messages shows an increasing buffer.
> > When it reaches 100% comes an EPG Error/Bug.
>
> The log messages you quoted show that vdr is unable to get the
> data written out as fast as they come in. 
> Obviously, this works better on channels with a lower data rate
> and worse on channels that require more data per second to be
> written to the hard disk.

Is that so. Use Pro7 very high data rates? What other channels are known
for high data rates; cause I've seen this at this time only at Pro7.

> Back to the real problem: Klaus has already answered it. It is most
> likely related to a lack of DMA on your /video disk. At least that
> is the most common reason why your disk is unable to accept the data
> as fast as they are coming in.

Its possible. hdparm saying DMA=on, but what is strange:

The recordings work a lot better (in fact at most channels no problem),
if the clock speed is 75MHz. But without DMA the CPU has to handle it,
and the recordings are all destroyed/unwatchable if the speed is over
75MHz. At 75MHz the vdr crashes, but the recordings are okay; no mpeg
artifact or anything like that.

The playing of some mpeg1/2 files works without problems; that was not
the case, when the CPU ran (more or less :) ) at 200MHz. I don't the the
reasonable connection between this MHz symptom

> I have posted a test program a while ago that shows you the effective
> read and write rate on your disk. Search the mailing list archives
> for disk_test.cpp and run this program on your disk. If it gives 
> you much less than 20MB/s, you do have a problem. If it uses over 90%
> of the CPU while writing, you almost certainly do not have DMA.

That was the result (how can I see the CPU use?):

> Reading.
> 969 MB.
> Read complete.
> 1016070144 bytes in 153.82 seconds = 6.29957 MB/s.

Not enough I guess...

> Of course there are other reasons besides "no DMA" that may slow
> down a disk while writing. A little known fact is that some manufacturers
> ship their disks with "write verify" enabled for a number of power
> cycles. For example, Maxtor does that. You can download a DOS program
> from their web site to turn "write verify" off, or you can simply 
> turn the computer power on and off about 20 times (not recommended)
> to get rid of it.

I will check that

> Other reasons include bad sectors, a driver problem
> with that disk type, other processes tying up resources, etc, etc.
> The fact of the matter remains: your data cannot get written as fast
> as they come in. Solve that problem and your recordings will work.

This is - like I said - a Maxtor 80GB HD. But my System Bios detect only
a 4GB HD - could this have something to do with it?

> It is almost certainly NOT a VDR bug.

I thought about a problem with my system.

Thanx
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