[mythtv-users] Opinion on a P4 Backend // HDD Throughput

[Jeff Holicky]

Thanks to all for your feedback - seems I am okay with my setup
and will give it a go.

Next is trying to price out a few FE's - for SD playback and
also, when it is time, to buy some more robust FEs for later HD
playback.
On the splitting of drives - I fully understand where you are all
going with that. I am developer and use Progress (transactional
database/language) [now called Open Edge]. All transactions are
written to the BI (before image) which then writes to the DB and
then the BI records are committed. Works great if the system is
shutdown or crashes since any partial transactions uncommitted
will be backed out automatically upon restart; client disconnect
etc.
Where I am going is that in a perfect world we would have a small
10GB HDD for the O/S; 5GB for logging; 10GB for the "BI" file and
then multiple drives for each "area" (part of the total DB).
Sadly the direction is bigger and bigger making such methods not
cost effective. SSD's (solid state) have issues with the number
of times being written to the same spot - logs would definitely
be an issue. I have read there are improvements to spread the
writes across different spots but that only works so much.
I was considering an SSD for the FE's - to cut down on heat and
noise - but even assuming there is little done by Myth with FEs
(writing out) there still are logs from the O/S. CD is a thought
(hate hate hate optics) but the concern is that it is a crap
shoot whether you get a drive that makes noise (like an airplane)
when accessed. HDDs - well back to the point of this email - I
would love a small HDD that is quiet and cool - even a 4800-5400
RPM would be sufficient for booting up. Haven't looked into that
- any thoughts? Cheap too - seeing as they don't have to be more
than say 5GB (something along the lines of the HDDs used by the
iPods perhaps). But then the burn is the size - small = more
money. I guess I can dream - but will still research that.
Q-Assuming one does a LOT of recording (not sure if there are
stats somewhere on this) - about how much disk space should
allocated to the myth database? I figure a 120GB - and divide it
into two - and use the non-OS/log side for archiving. Then have a
bunch of other HDDs for recording.  Are we talking up to 2GB; 5GB
or 10GB for the average DB?  I assume there is some
pruning/purging/compacting/reindexing routines.
Cheers all!
jeff
----- Original message -----
From: "Kevin Kuphal" <kkuphal at gmail.com>
To: "Discussion about mythtv" <mythtv-users at mythtv.org>
Date: Wed, 5 Mar 2008 16:32:51 -0600
Subject: Re: [mythtv-users] Opinion on a P4 Backend // HDD Throughput

On Wed, Mar 5, 2008 at 4:25 PM, Gareth Glaccum
<[1]gareth.glaccum at btopenworld.com> wrote:

----- Original Message -----
From: <[2]greg at nodecam.com>
>On my system (one firewire tuner, one PVR 250) I could cause
problems by
>recording HD, playing back the same HD stream on a delay and
recording SD
>at the same time. As soon as I put in a new disk and separated
recordings
>from database/logging, the problems went away.

  That doesn't really make sense. Logging and database access is
  a minimum in
  the situation you desribed (EIT scanning is about it I think),
  just moving
  the logs and database should have made little difference
  really.
  Ok, if you are running more than just myth, a lot of logging
  and seperate
  database accesses in the background then this would make a
  difference.


Myth writes *alot* of data for the seektables when recording. The
commflag process reads that as well as your playback so when you
start to get a handful of recordings, especially HD where the
bitrates are higher, the database gets hit pretty hard.

Kevin

References

1. mailto:gareth.glaccum at btopenworld.com
2. mailto:greg at nodecam.com
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