[CentOS] Question on server speed

Mon Aug 5 23:49:17 UTC 2019
Warren Young <warren at etr-usa.com>

On Aug 5, 2019, at 11:25 AM, Stephen John Smoogen <smooge at gmail.com> wrote:
> On Mon, 5 Aug 2019 at 13:17, Jerry Geis <jerry.geis at gmail.com> wrote:
>> Why is it that "all" I am really doing at the moment is copying things to
>> an external SSD disk USB3 connected and the machine "freezes"... Why is
>> that?
> You may have a motherboard which is routing a lot through a single USB
> controller. When that happens your graphical workstation will slow down
> because your keyboard and mouse events and some other polling has to
> complete before it can do the next thing.

Ridiculous if true.  Modern OSes solved the blocking I/O problem decades ago.

Consider: you may have a gigabit Ethernet connection to the Internet, and it is probably throttled to a small fraction of that speed by your ISP, yet you can be pumping hundreds of giga*bytes* per second to your SSD while your browser is blocked waiting for the remote server to respond.  Further, while one site is being slow to respond, another background Internet task can use the idled Internet connection.

This is a symptom of a real problem, and it may be well worth chasing it to the ground.

Jerry: Try another I/O channel for the same copy.  For example, what happens if you rsync the same file set to a remote machine, with the USB SSD connected to *that* machine?  Or, if you have a Thunderbolt or FireWire option, try that instead.  It might even be worth dropping a PCIe card into the machine for an alternative I/O path just to help diagnose this.  If nothing else, it might solve the problem.

USB is a terrible standard, emblematic of everything wrong with the PC world.  We were sold USB-C as the grand unification of Thunderbolt and classic USB, but what we actually got are 6+ different and partially incompatible flavors of USB-C!