RAID or not

[mickwall]

I am just about to start building a media server, the idea of this is it will run outside of the living area and have BTV 3.5 with multiple tuners. I will also put all my CD's etc on there as MP3 files.

The client PC (4 of them) will run BTV client and Beyond media when available and pull all the video/audo files from the new server.

I intend to have 4 * 250Gig drives and I was going to use RAID 5 to enable a disk failure without losing all my data. The OS will go on a separate drive.

My question is will RAID 5 reduce performance or not

Mick

[sho]

If you're using a hardware RAID card you shouldn't see any decrease over a normal PCI connected IDE controller, since the amount of data sent to the contrller /s is the same.

You're not so much conerned about anything exxcept your PCI bandwidth, and with multiple encoders, the easiest way to reduce that is to get cards with hardware encoders.

[theparanoid]

No raid five if it hardware based will give you better performance, but I am not sure if you realy need that increase. I am running one 250mb hard drive in quiet mode with 8mb and have notice zero probelms. Keep in mind however with Raid 5 you only be able to use 750GB of space. The last 250 will be used for fault tolerenace.

IF this is going to be software support raid 5 I would think twice about it, as in that case your likely run into performance issues.

[koan00]

Overall you _should_ see a performance increase mainly because you are going to be doing one or two write streams with multiple read streams.

My thinking is such:

Writing should be a bit slower (in a software raid setup) because every write is going to cause two bits to be written instead of one (the actual data bit and then the parity bit).

Reads will be faster because you are striping data over multiple disks.

So it seems the faster reads and data reliability will offset the nominal write penalty. The only problem is software RAID 5 cards are pretty rare and hardware ones are really expensive, what cards are you planning on using?

[sho]

Well I was really just talking about writes really, since if writes get bottlenecked, thats when you're going to see skips in your recording.

I was also refering to standard 32 bit PCI with it's half-duplex 133MB/s limitation. No matter what controller you've got or no matter how fast your drives are, thats going to be the ultimate bottleneck, especially since it has to then share that with the bit stream of your TV cards.

Thats the problem I always run into when the boss runs in with this new array controller. Sure, it can transfer huge amounts of data over it's U320 cables, but when it's sharing that bus with a 1Gb/s network card, even with 64 bit cards, I can't send files over the wire any faster....then they want me to add a second cotroller to an already swamped bus without giving the money for an additional machine....I'll spare you now

I'm not really saying that you won't see any increase (remember, I never ever speak of any software raid implementation), the increase in the simple a+b=c view is going to be minimal. In a more complex equation of capturing, compressing, streaming at the same time, maybe you'll really see an increase.


I'm just waiting for PCI Express to finally ship!

[mickwall]

The hardware I was looking at was 2 pvr 250's and an adaptec 4 port RAID card, either the SATA one or UDMA.

Thanks for all the comments

[pukka_parker]

Originally Posted by mickwall

The hardware I was looking at was 2 pvr 250's and an adaptec 4 port RAID card, either the SATA one or UDMA.

Thanks for all the comments

I have an adaptec 4 port (2 channel) RAID card (S-ATA) FS in UK if you want it. The box is opened, but I've not used it since I ordered SATA by mistake (cos I only have ATA drives). PM me if you would like to buy it for say 35 quid including P&P...

Regards.

Nigel

[koan00]

IIRC the Adaptec cards are all hardware based and all the ports are on the same card so you wouldnt be uneccesarily burden the PCI bus w/ the addition of a RAID device.

2 x PVR250 at highest setting = 25 Mbps [2x12Mbps vid + 2x384Kbps audio]

And I suppose you would need max of about 13Mbps for each client..

That might be a bit on the optimistic side, I am assuming one stream directly from PVR card to RAID and each client requires one stream from RAID to ethernet card.

PCI Bus = 1060 Mbps

So, I dont think the PCI bus will be too much of a bottleneck under normal usage.

Someone please correct me, this is wild speculation

[sho]

With the hardware encoders, as I said in my original post, there won't be any issue at all.