[mythtvnz] Drive throughput

[Steve Hodge]

On Sat, Apr 10, 2010 at 6:04 PM, AlanP <alan.p at orcon.net.nz> 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?
>

Yes, the Samsung will be enough. No, you don't need RAID 0.

DVB-S SD streams require about 2-2.5GB per hour: i.e. about 0.7MB per
second. A modern drive is capable of easily 35MB per second write speed (for
example). With only 4 transfers going at once you'd probably be fine even
with HD streams.

I don't regularly record three things at once but I have had two things
recording, one undergoing commercial detection and one being watched and
have never had any problems, even with the db and all recordings being on
the same three year old drive. This happened a lot during the olympics.

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.
>

I doubt drive bandwidth is the problem. It could be that you don't have
enough ram so are swapping. It could be database performance - having the
database on a different drive to the recordings is a good idea. The sort of
random access to files that databases do can significantly impact the
sequential read/write performance that video files typically enjoy.

Now that Myth has storage groups you'd be far better of not having those
drives combined with LVM or whatever. Just assign them to separate storage
groups and let Myth handle the load balancing. Keep one drive free for the
system and the database and everything will be great.

Cheers,
Steve
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