Make a dedicated partition on the drive that you use exclusively for
recording data. You can either read and write the partition directly
(i.e. no filesystem) or you could format it with a filesystem (xfs,
reiser, ext2, ext3). Most people prefer keeping things easy by using a
filesystem so let's consider that approach. Keep the partition empty.
The only file in the partition should be the file that is currently
being recorded. Once you have the file copy it to another partition if
you want to keep it. The point is to make sure the recording partition
is empty before starting a recording so the date file is contiguous on
the disk. File fragmentation can kill instantaneous recording speed. A
heavily fragmented filesystem may be able to average over 32 MB/s but
there will be times when the short-term transfer rate drops below 32
MB/s causing you loose samples. To compound the problem you probably
won't know how many samples you lost.
For the absolute best performance put the recording partition at the
front of the disk. The beginning of the disk is much faster than the
end. I've tested recent SATA drives at over 60 MB/s at the beginning of
the disk. Toward the end of the disk the performance can drop below 30
MB/s. As and example suppose your drive is 500 GB. Make the first
partition 50 GB and the second 450 GB. Use the first partition as the
recording partition and the second for storage and whatever. At 32 MB/s
the 50 GB partition will hold 26 minutes of continuous data. This is
obviously a "purist" approach but doing it this way you will have a
RELIABLE recording setup.
-Jim
Vincenzo Pellegrini wrote:
Hi all,
today I bought a 7200 rpm SATA HD
(a seagate barracuda, as Eric suggested some months ago)
in order to be able to sustain a complex 8Msps flow (32MB/s) towards the
usrp.
Once I formatted it with the XFS filesytem, following Rayan's tip, it
looked like I was getting the appropriate throughput...
is anybody using any other high performance filesystem to do this kind
of things?
..just to know if other options exist...
thanks
vincenzo
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