fractured playback

[Kristian Lam]

Hi Alisa,

The drives are not fast enough. A 1080i50 10-bit video will require about 132Mb/sec. Your drives are barely cutting it in terms of throughput, that’s why it’s choking.

regards

Kristian
Blackmagic Design

[Alisa Placas]

Thanks, Kristian.

Yikes. I thought uncompressed HD was around 100MB/sec.

What do I need to playback 8bit?
How much do I “lose” in 8 bit vs 10 bit? If I want to check for general image quality, color, motion and artifacting in these animations, could 8 bit be sufficient?

Alisa Placas
Lucid Animation
Cambridge, MA

[Alisa Placas]

I’m really not getting how this works.
I just got rid of all the unused media on the striped drives (quite a few gigs), reoganized it and reordered it with Disk Warrior.

Now, when I ran the Blackmagic Disk Speed Test, it says my read and write are around 98 MB/sec.
Why would I have LOST speed after cleaning out the drive?

Alisa Placas
Lucid Animation
Cambridge, MA

[Luke Maslen]

Hi Alisa,

Two disks are totally inadequate for uncompressed HD and you can see the data rates in the support note Storage and Data Rates for Uncompressed Video.

8 bit @ 1920 x 1080 @ 29.97fps = 119 MB per/sec, or 417 GB per/hr.
10 bit @ 1920 x 1080 @ 29.97fps = 158 MB per/sec, or 556 GB per/hr.

Even if your disk array just matched these speeds it would be inadequate. That is because a number of factors cause disk speeds to fluctuate. The more disks you have RAID’ed together, the smaller this variation becomes. Your 2-disk array will suffer from significant fluctuations.

In addition to the data throughput speeds mentioned above, the other big factor which is often overlooked is “seek time”. The more disks you have RAID’ed together, the smaller the seek time will be. Inadequate seek times will also cause poor performance and dropped frames. So even if your data throughput figures appear to be fine according to Blackmagic Disk Speed Test, your seek time might still be inadequate.

Your 2-disk array will be OK for standard definition uncompressed work but there is no way it can be used for uncompresesd HD work.

Your options are to either rapidly obtain a much faster disk array, such as any U320 SCSI disk array from Huge Systems, or else work in a compressed format. Fast disk arrays for uncompressed video will typically contain at least 8 disks and often more.

If you simply are not going to be able to obtain such a disk array in the time available, then consider using either the JPEG or DVCPRO HD codec. I would favour the DVCPRO HD codec as its quality is stunning at it support real time effects using Apple’s RT Extreme. This codec is so efficient you can even use it with a single FireWire drive but you would need your faster disk array for RT Effects.

The JPEG codec is even less demanding on disks but it doesn’t support RT Extreme in SD or HD resolutions and it doesn’t look quite as good as the DVCPRO HD codec at the default settings.

The only danger with using compressed codecs is if you need to do much rendering, then you may quickly see a loss of quality of the video. However if you are mainly just cutting video, then the quality will probably be perfectly adequate. DVCPRO HD is broadcast quality and might be a good immediate solution for you if you cannot quickly get your hands on a HD-capable disk array.

Regards,

Luke Maslen
Blackmagic Design