Updated: Jan 15, 2020
By: Patty Brogdon | February 28, 2019 | SANBlaze
Choosing which riser card to purchase in a SANBlaze SBExpress-DT (desktop), SBExpress-RM/RM4 (rackmount PCIe Gen3 or Gen4) or SBExpress-RMI (industrial version) depends on what features are the most important to you. SANBlaze offers both single and dual port riser cards that are manufactured either by SANBlaze or Quarch. While both types of cards offer many of the same features, the Quarch riser cards add the much sought-after capability of PCIe signal glitching and signal switching.
What is Signal Switching?
PCIe is a serial bus comprised of “lanes” where each lane is a data path to the device. Typical NVMe devices use from 1 to 4 lanes of PCIe to connect to the host bridge. Dual Path NVMe devices typically use two lanes for each of two paths.
An important test for an NVMe device is the response to a PCIe lane going “bad” or simply going away. The Quarch risers can remove any number of lanes for this type of exception testing.
For example, if you needed to test how an NVMe device would train if Lane 0 was missing, the Quarch risers can be programmed to disconnect Lane 0. Similarly, in the dual port test plan, it is desirable to remove Lanes 3 & 4 (both “B” lanes) and be sure that the device fails over to the remaining path without loss of data or functionality. Signal switching can be used to test Surprise Removal and Pull/Plug.
What is Signal Glitching?
A glitch is a spike or change in voltage in an electrical circuit, an unnecessary signal transition without functionality. While a bug is something that is known to be broken and needs a fix, glitches come and go randomly. As Alex Pieschel writes in Arcade Review:
“A bug is often cast as the weightier and more blameworthy pejorative, while glitch suggests something more mysterious and unknowable inflicted by surprise inputs or stuff outside the realm of code."
The Quarch single and dual port risers sold by SANBlaze support Pull/Plug, which physically disconnects the device under test from the PCIe bus through software by disconnecting all PCIe signals to the drive. The Quarch cards also support Signal Glitch which can simulate a glitch on the board in order to test the device under test’s response to random glitches or noise on the PCIe bus.
If you want to test how signal glitching affects your drives, the Quarch risers, although more expensive, are well-worth the higher cost.
For a complete list of the similarities and difference among the SANBlaze riser cards and the Quarch risers, in the Resources menu, click on the SANBlaze Riser Options PDF located in the Storage Testing Data Sheets from the Resources drop down menu.