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Re: [Discuss-gnuradio] UHD USRP Source for B2x0 overflows File Sink

From: Marcus D. Leech
Subject: Re: [Discuss-gnuradio] UHD USRP Source for B2x0 overflows File Sink
Date: Sun, 10 May 2015 17:18:58 -0400
User-agent: Mozilla/5.0 (X11; Linux x86_64; rv:24.0) Gecko/20100101 Thunderbird/24.2.0

On 05/09/2015 09:02 AM, Murphy, John wrote:
Marcus et al,

Had to drop this to do some work on another project yesterday, but
still want to pursue this just a little further if you don't mind,
because the numbers you are giving all look to me like it should be
able to be made to work.

You found my SDD sequential sustained write speed of 69 MBytes/sec.
If I attempt to save data at 14 MSamp/sec to disk with complex 16-bit
integers I believe there is an average long-term rate of 56 MBytes/sec
going to the disk.

So I am not understanding - it seems to me like I have plenty of
sustained throughput overhead to make this work, with the right
buffering to take up the temporary slack.

With 16 GBytes of RAM (the system is using some, but still) I would
expect that I can buffer up something like 4 minutes of data at the
required 56 MBytes/sec rate - seems like with the proper setup there
should be plenty of capability to ride through whatever other kernel
operations etc are momentarily stalling the disk writes.

Thanks, I appreciate you taking the time and list bandwidth to help me
understand this,
- John

You could try a simple experiment that tests your disk subsystem write performance without SDR stuff at all. Something like:

time dd if=/dev/zero of=some-file-on-your-disk bs=2000000 count=15000

This should write a 30GB file. The 'time' command will report how long it took. Then it's just a simple matter of math to figure out what your achievable long-term write rate is.

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