I posted my last entry meaning it to be the last thing I did yesterday before bed. Of course I couldn’t leave well enough alone, so I continued to tinker with Myth.
It turns out the OS X clients were definitely buggy and needed upgrading, as I posted before. However I never did get a good recording going, especially with the HD channels. There’s just too much data to be moved with a 1080i stereo datastream.
As mentioned before, my Myth box is running on an ancient motherboard, with a DMA66/33 IDE drive installed. I did some timing this morning of a few of my systems.
The Myth server’s drive is quite pokey:
hdparm -t /dev/sda
/dev/sda:
Timing buffered disk reads: 114 MB in 3.15 seconds = 36.16 MB/sec
My main fileserver, Maestro, has a SATA drive and clocks in twice as fast:
/sbin/hdparm -t /dev/sda
/dev/sda:
Timing buffered disk reads: 178 MB in 3.00 seconds = 59.32 MB/sec
Just for comparison, my Thinkpad is the slowest of all. The server I’m expecting to push the most bits, my Myth box, isn’t really much faster than a laptop. Pathetic!
hdparm -t /dev/sda
/dev/sda:
Timing buffered disk reads: 70 MB in 3.03 seconds = 23.10 MB/sec
So the mystery is solved: my MythTV backend is I/O bound. Being momentarily unemployed, I don’t have money to upgrade to a new motherboard/CPU with an onboard SATA controller. Once the paycheck drought is over, though, I’ll be fixing it up properly.
Interesting. I’m running my mythtv disk on an LVM volume and was curious what mine is running:
/dev/mapper/vg-lib:
Timing buffered disk reads: 142 MB in 3.02 seconds = 46.96 MB/sec
Interestingly enough, a SATA drive in the same machine not in a volume group records this:
/dev/sda:
Timing buffered disk reads: 232 MB in 3.02 seconds = 76.83 MB/sec
Then to compare, I went over to my desktop where my /home is a RAID 10 two drive setup:
/dev/md0:
Timing buffered disk reads: 154 MB in 3.02 seconds = 51.06 MB/sec
And for final comparison, the system disk in my desktop:
/dev/sdc:
Timing buffered disk reads: 228 MB in 3.02 seconds = 75.51 MB/sec
I’m not running anything HDTV at this point, but it looks like if I were to do that, I would probably want to move away from an LVM setup to a direct disk configuration.