[mythtv-users] Bad News for me...a warning to all

Fri Apr 23 18:47:09 EDT 2004

I don't want to start any religous wars (software vs hardware) but I'll
post my experiences.  

 As far as demands of video, HDTV is MAX 45Mb/s and an average HDTV
stream  is 17Mb/s.  If you only want one subchannel to be saved, it's
max 19.8Mb/s.  I had 3 PCHDTV cards writing to a single HD, and viewing
a stream without any performance problems (p4 3.2 Ghz w/ht) CPU load
from disk reading was 4% (JFS).  I current run raid 0 (Software) with
all three pcHDTV cards and can read (truely) 74MB (592Mb/s) and write 
24MB/s (192Mb/s).  A single drive is around reading 40MB's and writing
15MB's (7200RPM, 8MB cache).  You could be watching up to 12 MAX HDTV 
streams or recording 4 HDTV shows before you could have any problem,
guarentee'd, ever.  Realisticly, you can watch about 2-3 with the best
CPU (Because of decoding the video) and record 5 shows (Since the
average HDTV program is really around 17Mb/s) at once with ONE
harddrive.  Software raid has very little overhead, and works VERY well.
Raid 5 is always faster than a single drive.  (About 1.3-1.4 times as
fast to start off).  Raid 5 has to write 80% extra data for the
redundancy and so you have to figure that in.  But since you have 3
drives, raid5 has to be faster.  The best way to look at raid5 is it's
n+1, meaning you get n times the disk space and performance, +1 drive
that is wasted/used for redundancy.  I use raid 0 on my drives because I
don't care to spend extra $$ yet to have a drive for redundancy of HDTV
shows. .. not worth it yet.  Raid 0 gives me about 1.9x the performance
of a single drive.  I have 4 pci channels in my computer (using an extra
pci ide card) Single drive on each channel, (No slave drives.)  This
helps a little on performance.  When I have 6 drives, I won't need all
the performance I _could_ get because it's not needed.  Who is going to
be recording more than 5 HDTV shows at once to a single HD? Not anyone
probably... You'd fill the disk in a few hours.

 Also, at work I've had 2 promise tx2000 IDE cards go bad, one was
hardware was compeltely shot, the other had it's internal memory reset.
I did recover my data since I knew the settings of the card and you can
just plop a new card in and it works, but that can't happen (design)
with software raid.  I'll never touch an IDE raid card again if I can
help it, they're just too flacky to trust for "production".  Hardware
raid is always better, a lot more expensive too.  For me, software raid
provides enough speed benefits that I don't need to think about
hardware.  (IO on a HTPC will probably not be a problem we'll have to
deal with luckily).  

 Another thing to note about raid 5, it's not the raid level that makes
raid 5 slow, it's the drives.  IDE VS SCSI.  But again, you don't need
the performance like you're thinking you do.

--Brandon

On Fri, Apr 23, 2004 at 02:38:17PM -0400, Ed Benckert wrote:
> Software Raid 5 offers terrible performance... its ok for word documents 
> and the like, but theres no way the cpu/drives will keep up with the demand 
> of streaming continious MPG data to the drive, as well as reading it back 
> at the same time.
> 
> It's expensive, but a beautiful solution: Promise Technology Raid 5 ATA 
> controller cards. Here's a link to one:
> 
> http://www.cluboverclocker.com/reviews/raid/sx4000/
> 
> That is a 4 channel/4 drive card. I have the 6 channel/6 drive card. It's a 
> true hardware raid solution for ATA100/133 drives. I paid $250 for mine.
> 
> I do a lot of video editing and the like, and storing a DVD on a hard drive 
> eats up space, so I need a lot. When a drive goes bad and you have no good 
> soilution to back up a few 120 gig drives... you lose a lot of data and you 
> want to murder youself :)
> 
> I had a Highpoint Raid 5 controller card, but thats crap. It's basically an 
> ATA100 controller card with 4 controllers (8 channels/drives) that has 
> software raid built into the drivers. The performance was ABYSSMAL. I had 5 
> 80 gig drives in a 320gig raid 5 array, and I couldnt move my USB mouse 
> around the screen on my WinXP system without it pausing every second or so 
> as the CPU choked doing the raid computations.
> 
> The Promise card is a true hardware raid. And if I remember correctly, 
> comes with Linux drivers right in the box.
> 
> Oh, in addition you need to give it a DIMM for it's cache memory, there is 
> none on-board. It takes up to 128mb... so right now I have a 5 drive (80gb 
> each) RAID 5 system, 320gb of space, with a 128mb cache. It's beautiful.
> 
> And I've already had a drive go bad on me (it was 4+ years old). Bought a 
> new drive, popped it in, rebuilt the array... and my PC was back.
> 
> Love it. Cant reccomend it enough.
> 
> 
> Jason Donahue wrote:
> >Watch out for over heating everybody!!! I have (had) a micro-atx case
> >running my Myth setup...200GB Drive, and 2 tuner cards. All this in a
> >micro atx case generated a LOT of heat...I mean a LOT.
> >
> >Add to this, the enclosed cabinet wher my HT equipment is held...no
> >circulation.
> >
> >Well, easy to uess, my system got to hot...killed the power supply,
> >which in turn somehow fried my Hard Drive. EVERYTHING lost. ouch.
> >
> >I finally had every setting PERFECT. DAMN.
> >
> >Now I get to start all over. This time I will be using network storage
> >(nfs mounted from a data server, in a nice BIG and COOL case).
> >
> >Additionally, I plan on using software RAID 5, so I have the data
> >redundancy. I also plan on moving 1 tuner into the frontend box in my
> >bedroom...try to distribute the heat from those things.
> >
> >Anyway, thought I'd warn anyone out there...If your case seems really
> >hot - prepare for disaster.
> >
> >
> >
> >------------------------------------------------------------------------
> >
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