HTPC Bandwidth Santiy Check

[churcj2]

I'm designing(or maybe dreaming) of a HTPC built around sage. Currently I run a single tuner from my main computer into our old TV via long SVideo(ATI TVout) and Audio cables. It works, though quality suffers a little, but better than long play VHS (a little washed out).

I'd like to eventually have a dedicated PC close to the TV to run sage to the HTPC and also to acted as a sage server(and storage server) for the rest of the computers. I'm trying to work out some bottle necks.

1. Presumably 3 tuners (STDV) would be managable by the performance of a single harddrive (What's the average 30-40 MBits/s?). Wondering if it could also handle 1 or 2 read streams while writing the 3 streams. This would allow 2 people to watch TV from sage Clients/Server while 3 tuners are engaged in writing. Assuming close to DVD quality the transfer rate of each stream would be about 6-8Mbit/s. I'm thinking at this rate a single drive would be greatly taxed in trying to keep up with 5 of these streams (3 writes and 2 reads) not to mention that the disk head would be all over the place. Anyone know if a single drive can reasonably handle this? 5*6 would be 48mbs substained write/read streams which I would think tax most if not all single drive setups.

2. Assuming future proofing for HDTV, the bandwidth goes up to around 24Mbits? Would raid really provide enough bandwidth to handle a similar setup as above? 5*24=120Mbit/s

3. Can sagetv intelligently write to multiple disks? IE if you had 3 tuners have each tuner write to a different disk? This would be a reasonable way to manage bandwidth requirements.

4. I've looked at raid options. I suppose a stripped raid with enough drives (maybe 4) might provide enough bandwidth for HDTV 5 streams(3 write, 2 read). But reliablity of that many drives would be nasty so archiving is a bit time must (perhaps a must anyways). Any thoughts?

5. Would 2 HDTV streams saturated a 100mbit/s wired network? I think there is some overhead to the network, but presumably 48mbit/s is still well within the performance of a 100mbit/s assuming a reasonable fast CPU on the server.

I think that's all the questions for now. I have more but I'm still research and this is really too long for a single post as it is.

Thanks.

[blade]

The hard drive bandwith isn't an issue with SDTV. The capture rate is in Mbits while hard drive performance is measured in Mbytes so the disk isn't anywhere near it's limit.

I had 4 tuners and 1 drive when I first built my Sage server and had no problems recording 4 shows at 3.2 gig/hr, playing back a previously recorded show and processing shows with comskip all at the same time. All of this was done on a celeron 366 with 320 mb of ram and a single WD 7200 rpm 8mb cache drive.

[stanger89]

Originally Posted by churcj2

I'm designing(or maybe dreaming) of a HTPC built around sage. Currently I run a single tuner from my main computer into our old TV via long SVideo(ATI TVout) and Audio cables. It works, though quality suffers a little, but better than long play VHS (a little washed out).

I'd like to eventually have a dedicated PC close to the TV to run sage to the HTPC and also to acted as a sage server(and storage server) for the rest of the computers. I'm trying to work out some bottle necks.

1. Presumably 3 tuners (STDV) would be managable by the performance of a single harddrive (What's the average 30-40 MBits/s?). Wondering if it could also handle 1 or 2 read streams while writing the 3 streams. This would allow 2 people to watch TV from sage Clients/Server while 3 tuners are engaged in writing. Assuming close to DVD quality the transfer rate of each stream would be about 6-8Mbit/s. I'm thinking at this rate a single drive would be greatly taxed in trying to keep up with 5 of these streams (3 writes and 2 reads) not to mention that the disk head would be all over the place. Anyone know if a single drive can reasonably handle this? 5*6 would be 48mbs substained write/read streams which I would think tax most if not all single drive setups.

HDDs now are more like 40-60 MBytes/s, or about 8-10x more than your estimate. They aren't a problem.

2. Assuming future proofing for HDTV, the bandwidth goes up to around 24Mbits? Would raid really provide enough bandwidth to handle a similar setup as above? 5*24=120Mbit/s

OTA HD is max of 19.4Mbps, with many stations running subchannels, so, since Sage only records single subs, it's often more like 12-15Mbps.

QAM recordings (if we can ever do them) may be more depending on how their handled. A raw QAM channel is 36Mbps (which is actually 2 "normal" channels), but even then, it's not a problem.

3. Can sagetv intelligently write to multiple disks? IE if you had 3 tuners have each tuner write to a different disk? This would be a reasonable way to manage bandwidth requirements.

Sage records to whatever disk has the most free space. But as noted, bandwidth isn't a problem until you get into double-digit tuners.

4. I've looked at raid options. I suppose a stripped raid with enough drives (maybe 4) might provide enough bandwidth for HDTV 5 streams(3 write, 2 read). But reliablity of that many drives would be nasty so archiving is a bit time must (perhaps a must anyways). Any thoughts?

RAID-0 is a bad idea. Now if you need a lot of space (3+ drives worth) you might want to consider RAID-5. Just for capacity/redundancy/management reasons.

5. Would 2 HDTV streams saturated a 100mbit/s wired network?

I've timeshifted QAM with my MyHD to a (100Mbps) network drive, 36Mbps both ways, no trouble.

I think there is some overhead to the network, but presumably 48mbit/s is still well within the performance of a 100mbit/s assuming a reasonable fast CPU on the server.

Worst case scenario of 50% overhead (unrealistic really) you could still get at least 2 OTA channels simultaneously.

Moral of the story

100Mbps is plenty for streaming. Gigabit is awesome if you plan on copying files, and given the marginal price premium these days, go Gig if you can.

[churcj2]

Not sure why I thought harddrives were rated in MBits over MBytes. I guess I just got used to network measurements and such.

As I'm trying to keep my costs down I'll probably just opt for simplicity and get a single drive - 400-500Gig size. I could always add a second down the road. Maybe reuse an existing drive to run the OS and Virt Mem.

I thought about going raid, but raid adds complexity and cost and as a 3 tuner system would provide all of my needs quite comfortably I don't have a need for the performance boost. As this is a home operation, high availibility is nice, but not critical. Got to look into an effective, preferably automatic backup process - Not sure what's really reasonable given 500 - 1000G potential data. Any thoughts? Maybe another set of drives located in a seperate PC.

[stanger89]

Originally Posted by churcj2

I thought about going raid, but raid adds complexity and cost and as a 3 tuner system would provide all of my needs quite comfortably I don't have a need for the performance boost. As this is a home operation, high availibility is nice, but not critical.

My thoughts on RAID-5 in a home are that it's not worth it for speed, or availability. What it is good for (and about the only thing in a home environment) is providing massive amounts of contiguous storage (basically capacity beyond 2-3 HDDs) while minimizing risk of loss of data, or more accurately probably, mimizing risk of loss of time associated with collecting the replaceable data.

Got to look into an effective, preferably automatic backup process - Not sure what's really reasonable given 500 - 1000G potential data. Any thoughts? Maybe another set of drives located in a seperate PC.

While not for backup purposes, what I'm planning on getting (I need more space ) is one of these:
http://www.infrant.com/products_ReadyNAS_X6.htm
I know it supports some backup functionality, not sure if you need something PC side to do it in Windows.
There's a powerbuy getting setup on AVS:
http://www.avsforum.com/avs-vb/showt...&&#post6710968
Not sure what the final cost will be.

[churcj2]

I thought about a NAS solution as a possible backup option - not the most safe option but it would keep the data in 2 locations.

I noticed tomshardware has a writeup on turning an xbox into a linux based NAS, which might be a reasonable option for basic non raided storaged.

[stanger89]

There's just no cheap way to backup 1TB of data.

[Commodore 64]

hey stanger,

I PM'd the guy regarding that NAS box re: the group buy. Figuring around 600bucks for the thing. I doubt I can come up with that scratch, but that would be ideal for me. That's a cool product.

[salsbst]

Originally Posted by stanger89

There's just no cheap way to backup 1TB of data.

Agreed.

When I do get around to it, my current plan is to backup my array with hard drives. This will be made easier by the fact that the array is in a case with a lot of removable drive bays. But it won't be at a price that I'm happy about.

[salsbst]

Originally Posted by churcj2

I thought about a NAS solution as a possible backup option - not the most safe option but it would keep the data in 2 locations.

Two locations, yes, but probably both on the same power grid and in the same general physical location. It might be wise to keep the backup NAS off of the power/network grid when it is not in use, and of course moving it to a different building would be ideal.

I don't place enough value on my SageTV recordings to merit any of this concern, but I do have other files that I know I should be storing offsite. But I still don't do it. I hope I haven't jinxed myself by writing this down.