On Wednesday 09 March 2005 06:51 am, Pat Mac wrote: > I'm planning to convert my current p3 1 Ghz standard definition > backend into a firewire/hd backend (ATSC) and I just want to make sure > my thinking is correct. I don't want to convert this and then find > out I was off by a factor of 10 and my PCI bus is saturated. > > 1. Firewire & OTA streams come in at a max bitrate of 19.3 Mb or ~2.4 > MB per second > 2. Without gigabit ethernet, I can connect at max 4 frontends > 3. With multiple frontends I'm probably better off throwing a RAID in > the machine as well to maximize disk speed. > 4. Even with 4 streams coming in, 4 streams going out, and a hardware > RAID on the same PCI bus I'm not even close to maxing out the PCI bus > because I'm streaming in at ~10MB/sec, writing ~10 MB/sec to disk, > reading ~10MB/sec from disk, and writing ~10MB/sec to ethernet leaving > me with ~93 MB/sec still available on the bus and nothing to worry > about. > 5. Because the ATSC streams arrive pre-compressed in MPEG2, my system > will have no problem handling 4 of them since there is very little > processing going on > > Am I missing anything major here before I start? > Also, if anyone has Time Warner with a 3250, does the TW OSD show up > in the video from the firewire port? Can you set the output format > (say, send every chanel at 480p)? > > Thanks to everyone for the great system. > --Pat > Long time listener, first time caller.
Be careful of the network bandwidth. I was playing around this weekend with multiple slave backend configs. A 100mbps ethernet fell short doing: writing 3 - pvr250 records, 1 air2pc HD recording, and playing a HD recording on a remote NFS filesystem. If you simply add up the streams together, it might fit, but NFS is not efficient enough. I even multiplied the read and write buffering in myth by 10, used 8192 blocks, and nfs ver 3, but it wasn't quite enough. My network monitors showed 12-14 MBps (bytes), so I was swamping the network. So assuming the 4 hd cards are local to disk, you would still fall short streaming 4 hd shows out to frontends at the same time at 100mbps. I'm ording a gigabit switch right now. Keep in mind, both file system caching and NFS caching seem to bunch updates in bursts. If your frontend needs a read during that burst, it may have to wait. _______________________________________________ mythtv-users mailing list [email protected] http://mythtv.org/cgi-bin/mailman/listinfo/mythtv-users
