[mythtv-users] An LVM'd drive died! What do I do...

[Brandon Beattie]

On Thu, Oct 27, 2005 at 05:07:50PM +0100, Alexander Fisher wrote:
> Other hints ...
> Don't put more than one ide drive on a single ide channel.   A failing
> drive often takes out the bus.  SATA drives make sense, but SMART
> support for SATA is still under development.  You should also make
> sure that your SATA chipset has got linux support!

Do you have any references about this?  I've never seen this happen in
about 50 drives I've seen fail.  .. The only time I've seen more than 1
drive go out at once is due to an electrical problem in the system.
I've seen ruined drives on the same power cable, power supply, but not 
the same IDE channel.

SATA doesn't offer any performance that I see worthwile in a media box.
Having a single disk on an IDE port only helps if you're accessing two
drives at once.  Although this can happen in a media box, Myth doesn't
need it.  If you want to do it for fun that's one thing, but it's really
not needed.  As I've said before, I've saved 5 35Mb/s streams and watched
1 20Mb/s stream on a single 7200 RPM drive.  Myth buffers data when
storing to maximize storing to the FS.  I've pushed 99MB/s read and
65MB/s write to 4 drives (Using only motherboard ide channels).  That's
the equiv of 40 1080i streams read or writing 26HD streams at once
(Theoretical).  If you're going to be recording more than 8-10 HD
streams at once, or pushing 10+ HD streams to frontends then you may
want to start _thinking_ about SATA.  If you're doing SD then the
numbers I'd say would be 20 saving and 30 playback... (You'll max
network before having problems reading from a single drive).  Also, in
my testing, It was something like 10% slowdown when doing raid 0
striping and using two drives on the same ide channel.  However, if we
figure one drive gives us 100%, two drives give us 200%, then 10% loss
gives us 180% throughput, so you'll get more throughput if you put two
drives on the same channel rather than not using it at all.

SATA is good, but it's overkill.  SATA really shines if you're striping
drives, then it's very helpful to have it on it's own channel.  There's
no reason though that 99% of people should ever stripe drives for a Myth
box.  I did it for 6 months, it was fun to benchmark and show off.
However, your system is only as fast as the slowest point.  I've found
in HTPC's that your root partition and its FS, or the FS with the myth 
database on it make a more noticeable effect on usability.  XFS(best), 
then JFS, then Reiser4, then ReiserFS, then ext2, then ext3(worst) make
a large difference.  Brand of drives also makes a large difference (All
my Seagate drives run 15%-40% faster depending on the tests I run, over
the Maxtor ones I have).  I ran most all my tests on Maxtor's using XFS
as for how many streams I could push.

I currently have 4 HD tuners and 2 frontends in my MythBox.  I often
record 4 shows at once and while watching another.  I've chosen to go
with LVM for my 6 drives and 1.3TB of data.  I also picked ReiserFS (Not
reiser4, XFS, or JFS) because I've found shrinking a FS to be very
useful when dealing with a mythBox.  Since ReiserFS is really the only
FS that supports shrinking with LVM, I use it, even though it's the
worst performing for throughput.  I've never had a single problem with
disk throughput.  It's an AMD 2500, 512MB ram (It never uses over 120MB
unless it's commercial detecting, then it will use 300MB's).

Point is, if you're on a budget, there's no need to pay extra for 
"fastest" or "best" unless you're in a pissing contest.  I only
recommend paying more for reliability and suggest people get seagate
drives with a 5 yr warranty, and accept they will be faster and quieter
than maxtor, Western Digital, or other brands of HD's.

--Brandon