Newbie questions about disk usage and latency

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deajan
Posts: 3
Joined: Wed Jun 05, 2013 2:42 pm

Newbie questions about disk usage and latency

Post by deajan » Wed Jun 05, 2013 5:02 pm

Hello,

I just made my first zoneminder setup by compiling nextime's zoneminder v1.25 + multiple patches from http://www.zoneminder.com/forums/viewto ... =9&t=20587.
I've optimized the compilation for my atom processor (-O3 -march=atom -mtune=atom), which load doesn't exceed 0.5.
All images stored on a ZFS disk without compression.

I use two cameras i own, a LinkSys VWC54GCA and a Tenvis 319W.
Both cams work (one as RSTP source and the other as remote HTTP jpeg snapshoyt source).

My problem is about the latency i get on monitor.
When i set about 5fps, for each cam, i get like 10-15seconds latency before any motion appears on the screen, for both cams.
When i set 10fps, i get an acceptable latency.
But then 10 images saved to disk per second seems a bit high... I had a half hour of mocord for 2GB on disk... Seems high.
I've already lowered JPEG quality to 60 when no alarm is running.
I've also thought of enabling dedupe function of ZFS... but then, it's a low end atom processor, it will die trying to dedupe data.

I'm pretty sure there must be a "insert whatever the great think is" setting that makes everything work... But i can't figure out what to do...

Any advices please ?

mikb
Posts: 476
Joined: Mon Mar 25, 2013 12:34 pm

Re: Newbie questions about disk usage and latency

Post by mikb » Wed Jun 05, 2013 6:45 pm

deajan wrote: I've already lowered JPEG quality to 60 when no alarm is running.
I've also thought of enabling dedupe function of ZFS... but then, it's a low end atom processor, it will die trying to dedupe data.
If you're thinking the de-dupe of ZFS will help compress the image data, it won't work. No two images will be the same in any meaningful way, even if the camera is pointing at a static scene. Due to noise in the original image, every JPEG will be different, I don't think ZFS is smart enough to say that the files are JPEG's that are "near enough" the same :)

deajan
Posts: 3
Joined: Wed Jun 05, 2013 2:42 pm

Re: Newbie questions about disk usage and latency

Post by deajan » Wed Jun 05, 2013 7:09 pm

Yeah you're probably right about the zfs dedup option. Anyway, it would outperform the nano itx computer my setup runs on.
The zfs compression option ain't good to because jpeg is already compressed.

Isn't there anyway to store the events as h264 instead of single jpegs maybe?
Did i miss something?

bb99
Posts: 943
Joined: Wed Apr 02, 2008 12:04 am

Re: Newbie questions about disk usage and latency

Post by bb99 » Wed Jun 05, 2013 11:22 pm

When you lower your frame rate you need to adjust the pre buffer lower also. It's value is # of frames so unchanged at a value of 30 you'd have 3 seconds at 10 fps and 6 seconds for 5 fps.

deajan
Posts: 3
Joined: Wed Jun 05, 2013 2:42 pm

Re: Newbie questions about disk usage and latency

Post by deajan » Fri Jun 07, 2013 3:14 pm

Thanks for your answer...
But i have played a lot with the buffer settings, lowered about everything, also played with frame skipping... But i still get an ugly latency.
Anything that i may have forgotten ?

jameswilson
Posts: 5111
Joined: Wed Jun 08, 2005 8:07 pm
Location: Midlands UK
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Re: Newbie questions about disk usage and latency

Post by jameswilson » Sat Jun 08, 2013 8:07 pm

you can only use zm to set the fps if using jpeg grabs/capture cards. If using any other method you should not but a lower value in the fps setting than is being streamed. Limit at source if needed
James Wilson

Disclaimer: The above is pure theory and may work on a good day with the wind behind it. etc etc.
http://www.securitywarehouse.co.uk

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