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Re: [LUG] OT:To Raid or Not Raid (That is the Question)

 

On Thu, 27 Nov 2008, Dave wrote:

> Hi,
>
> Just wanted to garner people's opinion on whether or not to use RAID for 
> my Media Server.
>
> Basically I am not interested in Data Redundancy, Hot-Swapping etc - If 
> the machine goes down then I will restore from a regular backup and if 
> that takes a couple of days then so be it.
>
> What I am interested in though is fast I/O Throughput for Reading Data 
> because I want my Media Streaming (Music, Video etc) to be as fast as 
> possible and I am not sure whether it would be better to remain with a 
> normal Drive (probably SATA?) or to use RAID.
>
> My thinking behind this is that with certain modes of RAID you can have 
> the Data Striped across different disks and was wondering whether that 
> would offer any advantage during reading of data - Note either RAID or 
> not I'm not too bothered about Write Speed since most of the stuff will 
> be encoded once and simply stored (except obviously for TV Recording).

A single modern SATA drive will stream at upwards of 60MB/sec these days. 
Even faster at times. (I've seen 78MB/sec recently)

That'll give you room for 2 simultaneous full quality HD streams, maybe 3. 
Many many more for "regular" TV.

If pumping that data out over Ethernet, 100Mb is a shade over 12.5 
MBytes/sec max., so if streaming over your LAN, then you might need to 
consider Gb.

Going to RAID-0 will in-theory double your disk bandwidth. It'll also 
double the chances of failure, now that you need to rely on 2 drives for 
the data. RAID-1 will not give yo any speed-up whatsoever. (Actually the 
Linux R1 driver may give you a speed-up, but not by much)

So it'll boil down to money - buy 2 drives rather than one... reliability, 
(if one drive goes, you lose the lot), and the question over you really 
needing the speed...

And don't forget that the PCI bus bandwidth might be a limiting factor in 
cheaper motherboards too.

I'm currently building a box now with 2 drives in it, if I have time this 
afternoon I'll run some tests.

Gordon

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