Rendering and a dedicated drive–is it still desirable?

[Steve Rhoden]

My feeling is that the boot/system drive should ideally be separate from the drive used for rendering.

….It should.

Steve Rhoden
(Cow Leader)
Film Maker
Filmex Creative Media.
1-876-832-4956
https://filmex-creative-media.blogspot.com/

[Ron Bakker]

Just to clarify, are we talking about a render to location(drive) or a render from location?

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[Carl Alessi]

The dedicated drive would be for both the source footage, and the destination for the rendered version.

[Dave Haynie]

[Carl Alessi] “Right now, I’m having a debate with our tech guys about whether it’s necessary to make sure that I have a dedicated drive in the box just for rendering: they believe that at transfer speeds of 6 GB per second, having everything on SATA RAID 0 would be sufficient (they’re not sure that the Dell Optiplex they’re going to purchase will support RAID 0 plus a third, stand alone SATA drive internally).”

It’s not NECESSARY to have a second drive. It’s optimal, however.

And here’s the reality… the link speed of SATA 3.0 is 6Gb/s (six giga-bits per second) = 750MB/s. And even at that, a dual drive RAID0 isn’t going to perform anywhere close to that speed. You might get 100MB/s, maybe even 200MB/s. Probably not more.

Second issue… that’s “straight-line” speed. So if you have just one file, let’s say you’re getting 200MB/s. But one file isn’t very interesting. If you read one and render to another, that’s two files.
You can read at 200MB/s or write at 200MB/s, but not both to the same drive… so that’s a throughput of 100MB/s. Add a third file, and now you have to read two tracks, write one… now you’re 66MB/s throughput. And so on.

Only, no.. no soup for you. You’re not going straight-line anymore. Two files means seeking before each chunk of a file is read. So let’s say you have a two of those new WD 3TB drives, which haev an average seek time of 15ms. So for every full read/write (both files), you have 30ms of seek to factor in. So that 100MB of throughput is actually going to take 1 second + 0.030 second… so the throughput is actually 97MB/s, assuming 100MB buffers. But if you only buffered 10MB, that would be ten seeks per 100MB… 1 second + 30ms * 10 => 77MB/s.

What if you had three inputs and one output file being processed. Now it’s 50MB/s raw throughput, with four seeks per cycle… 1 second + 60ms => 47MB/s into a single 50MB buffer. But if you had only 10MB buffers, now it’s 1 second + 60ms * 5 -> 38MB/s.

And that’s only due to the RAID. RAID helps quite a bit in straight line performance. If one drive can read at 100MB/s, two ought to be close to 200MB/s… as long as they don’t exceed the link speed, which as pointed out first, they don’t. And better still, since you’re reading twice as much data before seeking within a file, even seeks are less of a factors.

But when you’re not straight-line… go into seeking between files. When a RAID seeks, all drives have to seek. And the data can’t be returned until they all finish seeking. So the seek time of the RAID is the worst-case of all drives at any given time. It’s almost certainly a little slower at seeks than a single drive.

The big complaint about single-drive systems in media editing goes way back to the early days of multimedia. In these days, memory was tight, and you could very easily have bits of a program or chunks of your own data paging from virtual memory to/from disc storage. Programs do virtual loads, DLLs get demand loaded, etc. Lots of possible other stuff going on. Put your data there too, and now the data, application, and OS stuff are all seeking all over the place. Better to move the speed critical stuff elsewhere.

Ok, but it’s 2011 now, almost 2012. Some of this isn’t important anymore, some it. You shouldn’t be paging. Sure, VM is turned on, but you have enough memory (or you can, anyway)… I saw a deal a couple of weeks ago for 16GB worth of DIMMs for under $60. But programs can still do virtual loads, DLLs can still load on-demand, and there’s other possible, normal OS activity. I don’t think it’s a big deal anymore, but you definitely want a second drive. Or more… I have a “project” drive, which is actually a drive bay. Drop a SATA drive in there, and it’s a video project, a backup drive, some archival stuff, etc. But I digress.

If you have a Solid State Drive, this is far less important. And even if you don’t.. while I have multiple drives, I often render to C:, and that’ll definitely go faster (assets on D:, outputs on C:) in pretty much any case than rendering one drive back to itself.

-Dave

[Carl Alessi]

Thank you, Dave. I wasn’t thinking about rendering back to the C: drive from the hypothetical D: drive, but your numbers make sense to me. I’ll pass this along. Thanks again.