Pegasus2: “superfast”?

[Chris Murphy]

FusionIo PCIe flash is at 1.5GB/s per card. Not accounting for encoding, yes two in a raid0 will saturate one TB2 controller.

I haven’t tested Core Storage “fusion drive” in anything other than a consumer type workload. If a read results in a cache hit, then you get SSD read speeds. If it’s a cache miss, you’d get the raid speed. The write speed would always start out at SSD speed, but for video this would end quickly (within 4GB of writing) as Core Storage doesn’t aggressively migrate data off the SSD. This might be enough to moderate the slow ramp up Bob Zelin reported elsewhere… maybe. But just like raid0, if the SSD drive dies, kaboom to all data, not just what was on the SSD.

Bcache on Linux shows some promise, as it does have some knobs unlike Core Storage, but it’s a bit early to support in production. However, it’s mainly write through for sequential writes, so that will avoid the SSD. Whereas any random io caused by metadata writes (?) would hit the SSD and at least not reduce performance on the raid made of HDDs. Those random IOs hit the SSD in write back mode, get aggregated, and written sequentially to the HDD. But then, on linux there are other options like Infiniband which probably obviate the need for a local SSD cache anyway.

[Alex Gerulaitis]

[Eric Hansen] “how would you propose building a DPX cache for the nMP? “

Here is one option:

LaCie Little Big Disk Thunderbolt 2, allegedly 1.4GB/s, consisting of dual 500GB PCIe SSDs in RAID0 in a TB2 box.

[Eric Hansen]

Thanks Alex. Macrumors quoted an article that briefly tested 2 of these enclosures in a RAID-0 and got 2GB/s Write and 2.4GB/s read. So yeah, that could work. Basically four PCIe SSDs spread over two TB2 connections.

Seems nuts to need that kind of speed, but I could see some of my 4k grading clients needing this. Since most 4k acquisition is raw and compressed (Redcode, F55), this wouldn’t be necessary for that footage. But for VFX shots in DPX, OpenEXR or TIFF, this could help. It could also help during export and DCP creation. It would also help if Resolve ever added the pre-cache feature that Baselight has (ie, if you have Redcode footage, it’s debayered and cached before you need it in grading, so the system can used the cached shot and doesn’t have to redebayer every time you manipulate a grade, so you don’t need a Red Rocket)

But then it makes me wonder what the latency of TB2 is compared to direct PCIe

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Eric Hansen
Production Workflow Designer / Consultant / Colorist / DIT
https://www.erichansen.tv