[mythtv-users] some more RAID and HD speed questions

[Jarod Wilson]

On Tuesday 17 January 2006 15:08, Steve Adeff wrote:
> On Tuesday 17 January 2006 18:00, Steve Hodge wrote:
> > On 1/18/06, Steve Adeff <adeffs at gmail.com> wrote:
> > > ok, its running great, is there a way I can tell what my max speeds
> > > are?
> >
> > hdparm -t
> >
> > I'm sure there are more sophisticated benchmark programs around as well.

# time dd if=/dev/zero of=/data/5gtest bs=1024k count=5120
5120+0 records in
5120+0 records out

real   1m56.057s
user   0m0.016s
sys     0m17.229s

That translatest to 5GB written in about 133 seconds, so 5120/133 is roughly 
38, or 38MB/s. Better benchmark than hdparm to see what sort of sustained 
writes your drive(s) can handle. Of course, what you're talking about is 
reading and writing simultaneously, but that gives you at least a rough 
ballpark of total bandwidth the drive can handle. You could try reading back 
that same 5GB test file, outputting to /dev/null, if you want to get a read 
performance baseline, then maybe average the two...

> > > also is there anything that can limit drive use in a similar way as
> > > nice can limit cpu usage?
> >
> > Do a search in the archives, I'm sure there have been threads
> > discussing powering down the drive when not in use. It's also a pretty
> > common requirement for laptops so there is definitely ways to do this.
>
> well, that I'm not so worried about, I mean more along the lines of how
> nice can limit a process from using cycles from higher leveled processes.

> > > I'd like to be able to copy some shows over the network to my other
> > > machine but to limit this such that no write operations are missed.
> >
> > I wouldn't worry too much. The disk throughput requirements of MythTV
> > are actually pretty low compared to the capabilities of modern
> > machines.

> well that depends on what your doing... I need to be able to record 2 HD 
> streams and 1 SD stream as a base, being able to playback an HD stream and 
> copy a file to another computer, but I'd like to be able to give priority to 
> the write operations to make sure I don't get any corrupted data due to high 
> usage.

Check out rsync. It has some bandwidth-limiting options that could be useful 
here... However, note that in my case, 38MB/s on sustained writes is more 
than 3x the bandwidth of a 100Mbps network (and still exceeds the throughput 
of many real-world GbE networks), so like the other guy said, drive bandwidth 
really shouldn't be an issue.

-- 
Jarod Wilson
jarod at wilsonet.com
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