Ultimately we want to be able to record high speed (with 12-15 Gbit/s throughput ) footage (uncompressed raw as DNG sequence) inside the AXIOM Beta to some sort of solid state media. This page acts as a hub to collect requirements, reasoning for/against particular aspects and solutions.

1 Datarates

12 Gbps = 1.5 GB/s

15 Gpbs = 1.875 GB/s

25 FPS DCI 4K (4096 × 2160) raw uncompressed 12 bit video datarate: 316.4 MB/s

50 FPS DCI 4K (4096 × 2160) raw uncompressed 12 bit video daterate: 632.8 MB/s

300 FPS 1920 x 1080 raw uncompressed 12 bit video daterate: 889.9 MB/s

100 FPS DCI 4K (4096 × 2160) raw uncompressed 12 bit video daterate: 1,265.6 MB/s

300 FPS DCI 4K (4096 × 2160) raw uncompressed 10 bit video daterate: 3,796.9 MB/s

2 SATA SSD

SATA 3.0 (6Gbit/s) requires Multi-Gigabit-Transceivers (MGTs) which are not available on the Zynq 7020. In addition it requires an Open Source FPGA implementation -> Elphel SATA2 implementation

2.5" SSDs with advertized write speeds of 450+MB/s start at around 0.25€/GB - 0.30€/GB (March 2017)

1.8" SSDs offer only very few models with 450+MB/s write speeds to choose from and prices are around 0.80€/GB - 1.90€/GB (March 2017)

2.5" SSD: 70 x 100mm

1.8" SSD: 54 x 78mm

3 PCIe SSD

This includes M.2 and CFast as they are based on the PCI Express interface. Requires Multi-Gigabit-Transceivers which are not available on the Zynq 7020.

M.2 SSDs connected over PCIe 3.0 x4 offering 1500+MB/s writespeed cost 0.40€/GB - 0.70€/GB (March 2017) and are the smallest and fastest option.

4 microSD card Raid

Since the interface for writing data to (micro)SD cards is pretty simple (electronically and protocol wise) the idea is to use an FPGA to act as raid controller and distribute high speed input data over N slower (~100MB/s write speeds) microSD cards. The raid controller should be able to define how many cards are used for parallel backups and how many for increasing throughput.

Price (microSD cards with > 90MB write speed - June 2017) is roughly: 0.60 - 0.80 € /GB

Dual Plugin Slot Module with total of 12 - 15 Gbps input

microSD card size: 11 x 15mm

When using a card slot holder like this we would utilize the available PCB space most effectively:

TF-Micro-SD-Card-Socket-Jack-Connector-Holder-Slot-Hinge-Type.jpg

Conclusion: Using 5 microSD cards in a raid gives roughly the same combined speed as using one 2.5" SSD. In this configuration the SSD is less than half the price per GB as the microSD raid at roughly the same physical dimensions.

When using 32 microSD cards in the raid it would require roughly 7x 2.5" SSDs in a raid to match the same speed resulting in roughly 7 times the volume of the microSD card raid.

5 e.MMC flash memory

cost: 0.80 - 0.90 € / GB (so similar to microSD cards) Looking at SanDisk SDINBDG4 e.MMC (SanDisk iNAND 7250 Industrial Embedded Flash Drives)

Size: 11x13mm

In comparison to the microSD card raid approach e.MMC has the following

Pros:

  • around 3x the write speed (300MB/s) per chip compared to one microSD
  • requires slightly less physical space (11x13mm compared to microSD cards: 11x15mm)

Cons:

  • chips are soldered on so individual chips cannot be taken out of the system like microSD cards could be (data recovery, changing capacity)
  • soldering these chips is likely outside our capabilities so we would need to have these boards populated externally - if we can use OSHPark to make the PCBs is currently in evaluation