[vdr] mdadm software raid5 arrays?

Steve steve-vdr at deltabbs.org
Thu Nov 19 14:37:46 CET 2009

Pasi Kärkkäinen wrote:
> You should use oflag=direct to make it actually write the file to disk..
> And now most probably the file will come from linux kernel cache. 
> Use iflag=direct to read it actually from the disk.

However, in the real world data _is_ going to be cached via the kernel 
cache, at least (we hope) a stride's worth minimum. We're talking about 
recording video aren't we, and that's surely almost always sequentially 
written, not random seeks everywhere?

For completeness, the results are:

#dd if=/dev/zero of=/srv/test/delete.me bs=1M count=1024 oflag=direct
1073741824 bytes (1.1 GB) copied, 25.2477 s, 42.5 MB/s

# dd if=/srv/test/delete.me of=/dev/null bs=1M count=1024 iflag=direct
1073741824 bytes (1.1 GB) copied, 4.92771 s, 218 MB/s

So, still no issue with recording entire transponders; using 1/4 of the 
available raw bandwidth with no buffering.

Interesting stuff, this :)


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