On 07/12/17 20:17, Richard Bradfield wrote: > On Thu, Dec 07, 2017 at 06:35:16PM +0000, Wols Lists wrote: >> On 07/12/17 09:52, Richard Bradfield wrote: >>> I did also investigate USB3 external enclosures, they're pretty >>> fast these days. >> >> AARRGGHHHHH !!! >> >> If you're using mdadm, DO NOT TOUCH USB WITH A BARGE POLE !!! >> >> I don't know the details, but I gather the problems are very similar to >> the timeout problem, but much worse. >> >> I know the wiki says you can "get away" with USB, but only for a broken >> drive, and only when recovering *from* it. >> >> Cheers, >> Wol >> > > I'm using ZFS on Linux, does that make you any less terrified? :) > > I never ended up pursuing the USB enclosure, because disks got bigger > faster than I needed more storage, but I'd be interested in hearing if > there are real issues with trying to mount drive arrays over XHCI, given > the failure of eSATA to achieve wide adoption it looked like a good > route for future expansion. > Sorry, not a clue. I don't know zfs.
The problem with USB, as I understand it, is that USB itself times out. If that happens, there is presumably a tear-down/setup delay, which is the timeout problem, which upsets mdadm. My personal experience is that the USB protocol also seems vulnerable to crashing and losing drives. In the --replace scenario, the fact that you are basically streaming from the old drive to the new one seems not to trip over the problem, but anything else is taking rather unnecessary risks ... As for eSATA, I want to get hold of a JBOD enclosure, but I'll then need to get a PCI card with an external port-multiplier ESATA capability. I suspect one of the reasons it didn't take off was the multiplicity of specifications, such that people probably bought add-ons that were "unfit for purpose" because they didn't know what they were doing, or the mobo suppliers cut corners so the on-board ports were unfit for purpose, etc etc. So the whole thing sank with a bad rep it didn't deserve. Certainly, when I've been looking, the situation is, shall we say, confusing ... Cheers, Wol Cheers, Wol
