On Tue, Nov 17, 2009 at 03:34:59PM +0000, Steve wrote:
Alex Betis wrote:
I don't record much, so I don't worry about speed.
While there's no denying that RAID5 *at best* has a write speed equivalent to about 1.3x a single disk and if you're not careful with stride/block settings can be a lot slower, that's no worse for our purposes that, erm, having a single disk in the first place. And reading is *always* faster...
Example. I'm not bothered about write speed (only having 3 tuners) so I didn't get too carried away setting up my 3-active disk 3TB RAID5 array, accepting all the default values.
Rough speed test: #dd if=/dev/zero of=/srv/test/delete.me bs=1M count=1024 1073741824 bytes (1.1 GB) copied, 13.6778 s, 78.5 MB/s
You should use oflag=direct to make it actually write the file to disk..
#dd if=/srv/test/delete.me of=/dev/null bs=1M count=1024 1073741824 bytes (1.1 GB) copied, 1.65427 s, 649 MB/s
And now most probably the file will come from linux kernel cache. Use iflag=direct to read it actually from the disk.
-- Pasi
Don't know about anyone else's setup, but if I were to record all streams from all tuners, there would still be I/O bandwidth left. Highest DVB-T channel bandwidth possible appears to be 31.668Mb/s, so for my 3 tuners equates to about 95Mb/s - that's less than 12 MB/s. The 78MB/s of my RAID5 doesn't seem to be much of an issue then.
Steve
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