[mythtv-users] Dual Core or Dual CPU??

[Sam Varshavchik]

GyroTech writes:

> Hello all - I'm looking for some hardware advice for a MythTV server I 
> want to build.
> 
> I'm looking to kit out a fairly beefy back-end, dealing with MythTV and 
> a file server. It's going to have a PCI-E RAID5 card in it (RocketRAID 
> seems to be a good choice there)and two, perhaps four, DVB-T tuner cards 
> in it. All the front ends will be FE-only boxes, maybe even diskless.
> 
> I was looking at forking out for a dual Opteron setup, but since these 
> Core 2 Duos have come out they seem to be able to handle a fair grunt. 
> So, has anyone worked with either\both setups care to give me an honest 
> opinion on what they would do. Obviously the Intel chips and lower power 
> and price on their side, but Opterons have the increased bus bandwidth 
> (which helps greatly in the transcoding) and redundancy on their side.

The CPUs are overkill. A PVR-x50 requires little CPU support. The PVR-x50 
hardware takes care of encoding without involvin the CPU, and MPEG decoding 
is not that demanding. There's nothing wrong with a dual Opteron, but if 
this is all you'll do, a Core 2 Duo will be fine. You should splurge for a 
dual Opteron only if you want to do some heavy compiling and building on the 
same machine.

On the other hand, forget about a RAID card. If that RAID card goes up in 
smoke, you'll need to replace it with an exact same one, otherwise the data 
on those disks will likely be inaccessible. You're better off using Linux 
software RAID. Hardware RAID cards, contrary to one's first impression, 
offer little performance benefit over softraid.

For the last ten years all my heavy I/O servers used SCSI disks, and I've 
been happy with them. My MythTV box is a recycled dual 500 Mhz Celeron CPU, 
with a SCSI drive. Works fine. I would recommend getting an Adaptec SCSI 
controller, and a pair of Seagate drives, then set them up as RAID-1, using 
Linux soft RAID. Don't waste money on a SCSI RAID model, just a regular SCSI 
card.

Not sure if you'll be able to do a hot-swap of a failed drive, with your 
hardware RAID card, but the Linux kernel has explicit support for disabling 
a SCSI device, on a running system, and reenabling it. The other day, one of 
my RAID-1 SCSI drive errored and Linux softraid disabled it, leaving the 
system running on the other drive completely. The drives are mounted in a 
hot-swap bay. I swapped it, enabled it, and resynced the RAID, all without 
taking the machine down. Whatever you do, put a pair of hot-swap drive bays 
in your server.

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