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

[Rudy Zijlstra]

Sam Varshavchik wrote:
> 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.

True, its why i tent to have a spare card lying around. Even so, i still 
prefer HW raid for system disks, as
1/ at the moment none of the disk based bootloaders handle partitioned 
raid (/dev/md0p0)
2/ i love the alarm on the cards, which will alert that a failure has 
happened. Important as i am not always around, and will warn other 
people to the problem
3/ with the drives mounted in hot-swap bays, a non-technical person can 
identify the failed drive and swap it.

So for me the advantage is not so much in performance, as it is in ease 
of management.

>
> 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.
>

Any half decent RAID card will let you do hot-swap, and will identify 
which disk has failed by permanently lighting  its led to  boot.

Cheers,

Rudy