SCSI Library

Q&A from “24G SAS: What’s New and How to Test It” Webcast

24G SAS » Webcasts

If you weren’t able to attend STA’s webcast titled “24G SAS: What’s New and How to Test It,” no worries – it’s available on demand here. We’ve also captured the questions asked and answers given by storage experts Mike Micheletti, Senior Product Manager, Teledyne LecCroy, and Cameron Brett, President of STA and Director of Enterpise Marketing, KIOXIA America Inc.

For some great insight, read on!

Q1. When will 24G SAS be available in the market?
A1. Production readiness is on track for 2020. The 24G SAS ecosystem continues to grow with analyzers (such as the ones from Teledyne LeCroy), cables, connectors, controllers, expanders, RAID adapters, HBAs, and SSDs that can take advantage of the 24G SAS features and capabilities. We expect 24G SAS-based server deployments to be on the market in the Q4 2020 timeframe.

Q2. Is there a 24G SAS Plugfest being planned?
A2. STA hosted the first 24G SAS Plugfest in June 2019 and is tentatively planning another plugfest for late 2020, with exact dates depending on restrictions due to the COVID-19 pandemic.

Q3. How do legacy 12Gb/s SAS storage devices connect to a 24G SAS fabric?
A3. SAS-4 still provides backward compatibility for legacy speeds and devices for two generations. On the upstream side of the expander, the link will still come up at the 24G rate, but when transferring data upstream from a 12G target, the expander has to reformat legacy 8b/10b traffic into the new SPL-formatted traffic. 24G bandwidth won’t be realized on the upstream link in this scenario. However, 24G SAS uses rate matching to provide backward compatibility with legacy devices by inserting scrambled idles or filler, such as ALIGNs. Any of the “deletable primitives” can be used as filler during rate matching. That’s how the 12G devices interconnect with the 24G hosts.

Q4. Are you allowed to mix primitive SPL segments within data segments?
A4. Within SSP frames, SAS-4 still uses deletable primitives like ALIGNs and the new Link Rate Management binary primitive for clock compensation. We’ll still see these with 24G traffic, and they can occur in the middle of an SSP frame, but not in the middle of an SPL segment. You can have ALIGNS inserted, but they have to be inserted as a separate SPL segment. That is still supported.