[mythtvnz] Drive throughput

[Stephen Worthington]

On Sat, 10 Apr 2010 18:04:33 +1200, you wrote:

>What would you all consider good in terms of enough performance for three 
>channels recording at the same time (off the Freeview DVB-S streams), while 
>also watching something from the same drive?
>
>Would a Samsung F2EG 1TB drive be enough? Should I go for a couple in Raid 
>zero, with another IDE drive I already have as the boot one?

I would be a little wary of the "eco" and "green" type drives.  They
are actually 5400 rpm mostly, although they can run faster sometimes.
I have WD 1.5 Tbyte green drive and it has wildly varying performance
with Vista - I can not predict if a given file transfer will be very
slow or very fast.  It is supposed to speed up to 7200 rpm as
necessary, but sometimes it does not even when copying a
multi-gigabyte file.  And the base speed when running at 5400 is
annoyingly slow.

I am currently using a Samsung HD103UJ (plain 7200 rpm drive, no
eco/green stuff) with everything except the swap partition on the same
drive.  With this drive, I find I am recording 4 programs at once at
least twice a week without any problems.  That would normally be a mix
of DVT-T HD, DVB-T SD and one Sky via MPEG2 hardware encoding (similar
data rate to TV1 HD at 720p).  On top of that I am playing back one
program and running two commercial skip processing jobs and while the
hard disk is busy, there is no sign that it is unable to cope.  MythTV
does run a bit sluggishly though when using the menus, but playback
once it starts is still smooth.

The drive specification that matters most is probably not the transfer
rate, but the access time, as when using the MythTV database and
running multiple recordings and so on at the same time, the drive is
spending most of its time moving the heads around.

I would recommend putting the system and database on one drive and
recordings on another if you can manage that.  Ideally having two
drives for recordings would be a good thing if you want to have good
performance in the menus while also doing lots of other things.  Myth
has options for whether you want it to spread activity around to
balance storage use, balance I/O activity, or balance both as best it
can.

My recordings partition is JFS (recommended), with everything else
ext3.  I do not recommend ext4 yet as it is much more liable to lose
data and get corrupted in emergency situations (such as power failure
or PC crash).

>I currently have a 160G IDE, and 2 320G SATA drives all lumped together in 
>Linux'es native what-ever-it-is setup, and at times in the evenings it gets 
>mildly laggy.

There appears to be a mild memory leak in mythfrontend at present, and
a really bad one in KDE's plasma-desktop.  That makes my box very
laggy unless I shut them down and restart them every so often to
prevent major swapping activity.  I have seen plasma-desktop using 1
Gibyte of RAM!