[vdr] Re: HDD access every 30 secs? (Slightly OT)

[Dennis Noordsij <dennis.noordsij@wiral.com>]

On Friday 04 October 2002 08:57, Christof Soehngen wrote:
> Hello there!
>
> I have question concerning my VDR box: Roughly every 30 secs, there is a
> HDD activity, I can see the hdd-led flash for a moment. This behaviour
> is even if VDR is doing "nothing".
>
> Now I don't want this behaviour because of the reduced lifetime of the
> hdd.
>
> My question: Is there anyway I can figure out who (which process) is
> accessing the disk and why?

Keep in mind the Linux kernel has a cache for disk read/writes, and possibly 
the disk itself has too. The every-30-second write is probably just a flush, 
so the real writes (which go to the cache) could happen several times within 
that 30 seconds. 

First thing for a VDR box is to mount everything with noatime, so the file 
access time does not get updated every time a file is read. You might look 
into metalog for a logger daemon which only writes to the logfile after it 
has collected a certain amount of data.

There are a few programs which will access the disk at some point, it depends 
on what you have running (on a dedicated VDR, less is better :-) DHCPD will 
keep it's leases up to date (stored in a file), for example.

Like Oliver said, the occasional write is not going to cause you any problems, 
spinning the disk and up down too much might.

If you feel like a bit of tinkering, you can extract the necessary files for 
VDR operations (some drivers, VDR, some libraries) to a RAM disk (so a very 
minimal Linux distro - use tmpfs if you can) and only mount a video partition 
to disk. I guess then you can be sure only VDR will access the disk, and only 
when it is doing something. 

You could then, if your hdd and chipset support it, set a time-out for the 
drive where it will spin down the drive. It will cause a small delay when you 
start a recording, but for example an automatic recording has enough time at 
the beginning of the timer to comfortable spin up the drives. You'll lose 
some data there, but most likely it's just commercials :-)

Or possibly even better, if your drive has acoustic management you can tell it 
to switch to its lowest-noise level. It only needs to stream 500kB per second 
for a recording, my 5 year old WD does 12 MB/sec on a 7 yr old motherboard 
:-) (I'll admit I was quite surprised!)

If you have more than 1 drive, don't RAID-stripe them, the speed gain is 
completely unneccesary for VDR use, and requires both drives to be active 
during recording and playback, where 1 drive would do just fine and the other 
could be spun down or whatever. VDR handles multiple drives like that 
perfectly I understand (haven't tried it though :)

Maybe other people with dedicated VDR's would like to comment on HD setups 
etc? :-)

Cheers,
Dennis




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