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240 EpisodesProduced by Jupiter BroadcastingWebsite

Systems, Network, and Administration Podcast. Every two weeks TechSNAP covers the stories that impact those of us in the tech industry, and all of us that follow it. Every episode we dedicate a portion of the show to answer audience questions, discuss best practices, and solving your problems.


408: Apollo's ARC

We take a look at the amazing abilities of the Apollo Guidance Computer and Jim breaks down everything you need to know about the ZFS ARC.

Plus an update on ZoL SIMD acceleration, your feedback, and an interesting new neuromorphic system from Intel.


  • ZFS On Linux Has Figured Out A Way To Restore SIMD Support On Linux 5.0+ — Those running ZFS On Linux (ZoL) on post-5.0 (and pre-5.0 supported LTS releases) have seen big performance hits to the ZFS encryption performance in particular. That came due to upstream breaking an interface used by ZFS On Linux and admittedly not caring about ZoL due to it being an out-of-tree user. But now several kernel releases later, a workaround has been devised.
  • ZFS On Linux Runs Into A Snag With Linux 5.0
  • NixOS Takes Action After 1.2GB/s ZFS Encryption Speed Drops To 200MB/s With Linux 5.0+ — A NixOS developer reports that the functions no longer exported by Linux 5.0+ and previously used by ZoL for AVX/AES-NI support end up dropping the ZFS data-set encryption performance to 200MB/s where as pre-5.0 kernels ran around 1.2GB/s
  • Linux 5.0 compat: SIMD compatibility · zfsonlinux/zfs@e5db313 — Restore the SIMD optimization for 4.19.38 LTS, 4.14.120 LTS, and 5.0 and newer kernels. This is accomplished by leveraging the fact that by definition dedicated kernel threads never need to concern themselves with saving and restoring the user FPU state. Therefore, they may use the FPU as long as we can guarantee user tasks always restore their FPU state before context switching back to user space.
  • no SIMD acceleration · Issue #8793 · zfsonlinux/zfs — 4.14.x, 4.19.x, 5.x all have no SIMD acceleration, it is like a turtle. very slow.
  • Chris's Wiki :: ZFS on Linux still has annoying issues with ARC size — One of the frustrating things about operating ZFS on Linux is that the ARC size is critical but ZFS's auto-tuning of it is opaque and apparently prone to malfunctions, where your ARC will mysteriously shrink drastically and then stick there.
  • Software woven into wire, Core rope and the Apollo Guidance Computer — One of the first computers to use integrated circuits, the Apollo Guidance Computer was lightweight enough and small enough to fly in space. An unusual feature that contributed to its small size was core rope memory, a technique of physically weaving software into high-density storage.
  • Virtual Apollo Guidance Computer (AGC) software — Since you are looking at this README file, you are in the "master" branch of the repository, which contains source-code transcriptions of the original Project Apollo software for the Apollo Guidance Computer (AGC) and Abort Guidance System (AGS), as well as our software for emulating the AGC, AGS, and some of their peripheral devices (such as the display-keyboard unit, or DSKY).
  • The Underappreciated Power of the Apollo Computer - The Atlantic — Without the computers on board the Apollo spacecraft, there would have been no moon landing, no triumphant first step, no high-water mark for human space travel. A pilot could never have navigated the way to the moon, as if a spaceship were simply a more powerful airplane. The calculations required to make in-flight adjustments and the complexity of the thrust controls outstripped human capacities.
  • Brains scale better than CPUs. So Intel is building brains | Ars Technica — Neuromorphic engineering—building machines that mimic the function of organic brains in hardware as well as software—is becoming more and more prominent. The field has progressed rapidly, from conceptual beginnings in the late 1980s to experimental field programmable neural arrays in 2006, early memristor-powered device proposals in 2012, IBM's TrueNorth NPU in 2014, and Intel's Loihi neuromorphic processor in 2017. Yesterday, Intel broke a little more new ground with the debut of a larger-scale neuromorphic system, Pohoiki Beach, which integrates 64 of its Loihi chips.
  • Dancing Demon - YouTube — Written in 1979 by Leo Christopherson for the Radio Shack TRS-80 Model I computer. This is the best game ever for at that time.
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