RAID Benchmark Spikes - Is this normal?

[shoodogg1977]

Highpoint Rocket Raid 2320
8 x 250 GB SATAII hard drives in a RAID0 array

After running HDTach, I get this image and results:

I'm concerned about the image itself. Is it normal for a RAID array to spike up and down like that? If I run HDtach on my regular SATAII drive, it starts out at a high number and slowly slopes downwards as it reaches the end.

Any thoughts on this?

Thanks, Scott

 

[shoodogg1977]

I updated the image to show both tests. The Red line used 8mb zones and the blue line is 32mb zones.

-Scott

 

[unhappy_mage]

In a word, yes. Even expensive Areca IOP341-based cards have graphs like this in HDTach.

Edit: 8-disk raid 0? Is this data backed up? Should it be?

 

[shoodogg1977]

OK. I'll stop worrying about it. Thanks for the reply!

-Scott

 

[unhappy_mage]

In case you miss the edit, is that data backed up? If it's not something you're prepared to lose, you should back it up. An 8-disk raid 0 array is more than 8 times as likely to lose data from disk death as a single disk.

 

[drizzt81]

I would have expected an eight-disk RAID-0 array to show a higher STR.

 

[shoodogg1977]

Hi Mage,

The RAID array is only for video capture from my Decklink HD Extreme card for editing. The final rendered files are placed on a stable hard drive. If the RAID crashes, I simply re-capture the footage.

The problem is that I have been getting dropped frame errors while capturing footage and I was wondering if it was due to those spikes I saw. I thought that maybe if the drive suddenly dipped down to 80 mb/s it would cause the dropped frames.

Hi Drizzt,

What is an STR? What would be causing it to be low and how would I go about changing it?

BTW, when I use the Blackmagic Disk Speed Test, I get a Data Read at 443 MB/s and a Data Write at 439 MB/s.

 

[unhappy_mage]

Hi Mage,

The RAID array is only for video capture from my Decklink HD Extreme card for editing. The final rendered files are placed on a stable hard drive. If the RAID crashes, I simply re-capture the footage.

Ah, good. Just making sure you're not keeping your irreplaceable wedding photos on it or something

The problem is that I have been getting dropped frame errors while capturing footage and I was wondering if it was due to those spikes I saw. I thought that maybe if the drive suddenly dipped down to 80 mb/s it would cause the dropped frames.

That's a possibility. What data rate is the video that's captured stored at? The website linked mentions 1.485gbps video, which is 185 megabytes per second. That could probably cause the dropouts. Is the video captured compressed or uncompressed? How much CPU is used while capturing?

What is an STR? What would be causing it to be low and how would I go about changing it?

Sequential Transfer Rate. Since you write the video data in order to a file, the hard drive won't have to seek all over the place very often.

PS: Welcome to [H]!

 

[shoodogg1977]

Hi Mage,

The bit rate is around 30 MB/s. I don't know what that equivalates to in megabits. It is using the component video cables on the Decklink to capture 1080i 4:2:2 HD video streams but using the blackmagic codec to compress them. So it isn't full 4:4:4 uncompressed HD.

I just did a quick capture test and the CPU never goes above 20%. I have two Xeon 5130's and 4 GB of 667 FBDimms.

The MB is a Tyan 5000XL.

If it isn't the RAID array, maybe it is some kind of PCI bus conflict or bottleneck. I only have three things pluged into my PCI x slots. The RAID controller, my Nvidia graphics card and the Decklink card.

I don't know how to test the STR. Even if I did, I don't know how to make changes to it.

I wonder if anyone else on here has a similar setup and what there average read/write is using HDTach? That would tell me if I should invest more time into seeing if something is actually wrong, like a bad drive or something.

And, thank you very much for the warm welcome! I think it's the first time I've ever been welcomed into a forum.

-Scott

 

[unhappy_mage]

Hi Mage,

The bit rate is around 30 MB/s. I don't know what that equivalates to in megabits. It is using the component video cables on the Decklink to capture 1080i 4:2:2 HD video streams but using the blackmagic codec to compress them. So it isn't full 4:4:4 uncompressed HD.

Hmm. You should definitely be able to handle 30 MB/s, even if you had just one disk. If you have time, you could break the array and hook the drive to a different controller, then see if capturing to a single disk works. I know you'll probably need more space than one disk provides, but it'll eliminate the card as a possible problem.

I just did a quick capture test and the CPU never goes above 20%. I have two Xeon 5130's and 4 GB of 667 FBDimms.

The MB is a Tyan 5000XL.

Yeah, I would kind of expect that to handle this kind of load. Although I've had problems with Tyan boards and their interactions with storage adapters in the past, I can't say this looks like their fault. Doesn't mean it isn't, of course, but I wouldn't worry about it first.

I don't know how to test the STR. Even if I did, I don't know how to make changes to it.

HDTach tests STR. 160 MB/s is more than 30 (and the 400 some the Blackmagic thingy reports is even more ) so unless your application is doing something strange with regards to writes I can't imagine what's causing problems.

Do other video capture applications work with the DeckLink card? VirtualDub does a good job writing to disk in a logical fashion, so if there are VfW drivers for that card you might try it instead.

And, thank you very much for the warm welcome! I think it's the first time I've ever been welcomed into a forum.

Yeah, yeah. Just don't expect this every day

 

[shoodogg1977]

Hmm. You should definitely be able to handle 30 MB/s, even if you had just one disk. If you have time, you could break the array and hook the drive to a different controller, then see if capturing to a single disk works. I know you'll probably need more space than one disk provides, but it'll eliminate the card as a possible problem.

I have about 1 TB of video files on it right now. As soon as I am finished with this client I will start removing drives and doing more tests. I might even try the onboard RAID and see if I get better results. The problem is that I have a system drive, a render destination drive and only 6 ports on the MB. So, if it is the Highpoint card I will only have 4 ports to work with. That limits me to 1TB which fills up fast around here.

HDTach tests STR. 160 MB/s is more than 30 (and the 400 some the Blackmagic thingy reports is even more ) so unless your application is doing something strange with regards to writes I can't imagine what's causing problems.

The Blackmagic disk test takes into account the RAM cache. I think that is why it is so high. Which might also explain what is happening. For example, if the Decklink card is putting some of the transfer stream into RAM, it may drop frames when the RAM fills up and has to wait for the RAID to write the files.

Do other video capture applications work with the DeckLink card? VirtualDub does a good job writing to disk in a logical fashion, so if there are VfW drivers for that card you might try it instead.

I have tried the Vegas capture utility which uses VFW drivers and saves the files as .avi. It still drops frames. I have a copy of virtual dub and will give that a try as well.

Yeah, yeah. Just don't expect this every day

Oh, yeah. I forgot you were an un-happy Mage.