RAID suggestions...

[Ashley M. Kirchner]

    I'm looking at setting up a RAID system for doing video work.  My 
two main requirements are speed and reliability.  Speed is an issue 
because of the constant streaming of hundreds of megabytes, if not 
gigabytes of data that is inherent with video.  And obviously 
reliability, I want to make sure I don't lose any data of a drive 
crashes on me.  This will also be a hardware RAID solution (as opposed 
to software) and, depending on funds, I may try to make it a 
hot-swappable system.

    Based on all the different RAID levels out there, what does the 
collective suggest?  1? 3? 5? 0+1?

[Bruno Wolff III]

On Sun, Dec 31, 2006 at 19:48:23 -0700,
  "Ashley M. Kirchner" <ashley(a)pcraft.com&gt; wrote:
>  
>     I'm looking at setting up a RAID system for doing video work.  My 
>  two main requirements are speed and reliability.  Speed is an issue 
>  because of the constant streaming of hundreds of megabytes, if not 
>  gigabytes of data that is inherent with video.  And obviously 
>  reliability, I want to make sure I don't lose any data of a drive 
>  crashes on me.  This will also be a hardware RAID solution (as opposed 
>  to software) and, depending on funds, I may try to make it a 
>  hot-swappable system.
>  
>     Based on all the different RAID levels out there, what does the 
>  collective suggest?  1? 3? 5? 0+1? 
Raid 5 is generally good for mostly read situations, though you may want
to do some bench marking to see if you really need that. More spindles
are better than fewer spindles. Normally you would use raid 10 in preference
to raid 0+1, since raid 10 handles failures better. If are capturing video and
not publishing it, than raid 10 is usually better than raid 5 unless you have
a fair number of spindles.

I wouldn't be too quick to dismiss software raid. Generally unless you spend
good money to get a raid card with battery backed cache, you are better
off with software raid. In your case you might have a cpu bottleneck
depending on what processing you are doing of the video. In that case you
would be more inclined to go with hardware raid, but you would want to
look at the cost of buying more cpu versus the cost of a better raid card.

You should be able to rough out some numbers to see what you need to do
what you want. You should be able to figure out what data transfer rates
you need and then test the bandwidth for individual disks to get an estimate
of how many spindles you need. And you should be able to compare that
to the bandwidth supported by the controllers you are considering. If you
have really heavy demands, you may need multiple controllers.

Be careful with the write cache settings of your drives. If you are using
software raid, you can leave write caching enabled if you use write barriers.
A good raid card should properly handle write caching for you, but you
might want to do some sanity tests to make sure that writes aren't being
reported as complete when they are actually just in the drives' cache.

[Fedora] Re: RAID suggestions...

[Ashley M. Kirchner]

Bruno Wolff III wrote:
>  Raid 5 is generally good for mostly read situations, though you may
> want
>  to do some bench marking to see if you really need that. More spindles
>  are better than fewer spindles. Normally you would use raid 10 in preference
>  to raid 0+1, since raid 10 handles failures better. If are capturing video and
>  not publishing it, than raid 10 is usually better than raid 5 unless you have
>  a fair number of spindles.
>     
    In my case, I will be capturing video, editing, and then authoring 
DVDs.  So the streaming during capture and editing is important.  The 
authoring of the DVD not so much because it can only stream as fast as 
the drive can write.  But everything else needs to be able to keep up.


>  In your case you might have a cpu bottleneck
>  depending on what processing you are doing of the video.
>     
    I'm not worried about that.  At the moment I'm using a Core 2 Duo 
Extreme and will eventually bump that up to a quad core.  The old system 
had a Core 2 Duo 2.6GHz and it worked wonderfully.

    -- A

[Bill Davidsen]

Ashley M. Kirchner wrote:
>  
>     I'm looking at setting up a RAID system for doing video work.  My two 
>  main requirements are speed and reliability.  Speed is an issue because 
>  of the constant streaming of hundreds of megabytes, if not gigabytes of 
>  data that is inherent with video.  And obviously reliability, I want to 
>  make sure I don't lose any data of a drive crashes on me.  This will 
>  also be a hardware RAID solution (as opposed to software) and, depending 
>  on funds, I may try to make it a hot-swappable system. 
fast - reliable - inexpensive. pick two.

But unless you are running multiple video feeds into the disk at one 
time, fast isn't an issue. Commodity SATA drives will do 50MB/s without 
effort, and 200MB/s is readily reached using software RAID. If you want 
fast and reliable, go SCSI. Until recently I ran 20+ servers for an ISP, 
with 6M users, and 2-6TB/server. There isn't a non-SCSI RAID card I can 
recommend (that does NOT mean they don't exist, I just didn't find one).

If 150MB/s write and 200+ read with good reliability will do, go 
software RAID-6 for the data, RAID-1 (three way if you're paranoid) for 
the o/s and swap.

Hardware RAID is very good, but the "firmware RAID" on motherboards and 
cheap controllers are not usually fast OR reliable enough. Use a lot of 
memory. No, more than that.
>  
>     Based on all the different RAID levels out there, what does the 
>  collective suggest?  1? 3? 5? 0+1?
>   
cheap: RAID-5
reliable: RAID-6+hot spare
fast and reliable: RAID-10+2xhot spare, RAID-1 for bot/root/swap

For SCSI I have had good luck with the "ServeRAID" IBM controllers. 
They're Adaptek with IBM firmware hacks, I believe.

-- 
Bill Davidsen
   He was a full-time professional cat, not some moonlighting
ferret or weasel. He knew about these things.

[Fedora] Re: RAID suggestions...

[Ashley M. Kirchner]

Bill Davidsen wrote:
>  fast - reliable - inexpensive. pick two. 
    In order of
importance, I would put "expensive" as last, with fast 
and reliable being the top ones.  This doesn't mean it has to be an arm 
and a testicle expensive, but at the same time I'm okay with spending a 
couple of thousands building it up (over time).

>  But unless you are running multiple video feeds into the disk at one
>
>  time, fast isn't an issue. 
    I guess it depends on how you look at it.  I can
be encoding one 
feed, and watching another at the same time, or encoding and importing a 
second feed (from camera).  And while I realize that the encoding part 
is primarily CPU intensive, the disk does get taxed at the same time as 
it's writing frames out.  And if I'm importing another feed at the same 
time, the drive will pull double duty.  So if I'm going to be using the 
same cluster of drives for this, it would have to be able to keep up 
with that.

    The other option is to build two separate, smaller RAID 
configurations and use one for importing feeds and the other to encode 
on.  With a quad core CPU, it'll come down to other bottlenecks in the 
whole architecture, be it bus speed, network traffic, or simply how fast 
the camera's feeding data in.

>  Commodity SATA drives will do 50MB/s without effort, and 200MB/s is 
>  readily reached using software RAID. If you want fast and reliable, go 
>  SCSI. 
    While I don't have anything against SCSI drives, except for the high

cost, is there any particular reason why you prefer SCSI over SATA II?

>  For SCSI I have had good luck with the "ServeRAID" IBM
> controllers. 
>  They're Adaptek with IBM firmware hacks, I believe. 
    Adaptec is already on
my list of vendors. :)  Thanks for the 
confirmation.

    - A