[geeks] Disk to Disk Caching

[Sridhar Ayengar]

Joshua D. Boyd wrote:
>>>> Ok.  I have this Lacie Firewire 800 external RAID 0 hard disk.  The 
>>>> drive is just *barely* fast enough to stream compressed HD video. 
>>> What compression are you using and at what bitrate?
>> I'm not sure of the bitrate.  I'd have to go check.  Some of the stuff 
>> is MPEG-2 and some are VC-1.  All of it is in 1080p format.
> 
> 1080p23.97, 1080p24, 1080p25, 1080p30, 1080p50, 1080p59.94, or 1080p60?

Either 1080p59.94 or 1080p60.

> Assuming that you MPEG2 is coming from HDV, it shouldn't be any higher
> than 25Mbit/second, which is a little over 3 megabytes a second.  I find
> it difficult to believe that you FW800 disk array can't keep up with a
> modest number of simultaneous FW800 streams.

Ok.

> Were you using XDCAM-HD, that goes up to 35Mbit/sec, but that is still
> only 4.3MByte/sec.

Ok.

> Now, VC-1 can go up to 135Mbit/sec, which is nearly 17Mbit/sec, but even
> two streams of that should easily be within the realm of doable for a
> FW800 array (provided that it wasn't built using 7 year old disks).

Does it matter that the FW800 card is sitting in a 32-bit 33MHz PCI 
slot?  If so, I might invest in a PCIe x1 FW800 card.

> Have you tried benching the transfer speed of the array to look for
> malfunction there?

No.  That's a good idea.  I'll try that.  I have been noticing a very 
high CPU usage whenever I'm pushing data as fast as possible onto it. 
Maybe my FW800 drivers suck.  If this is indeed the problem, are there 
any FW800 for 64-bit Windows you might recommend?

As you can probably tell, this is the first time I'm doing anything like 
this, and I'm still figuring this stuff out.

Peace...  Sridhar