On 2016-01-25 16:12, Chris Murphy wrote:
On Mon, Jan 25, 2016 at 9:43 AM, Austin S. Hemmelgarn
<ahferroin7@xxxxxxxxx> wrote:
Now, just a general caution: Avoid using USB storage for persistent online
storage, there's just to many things that can go wrong, and quite a few USB
storage controllers are absolute crap.
Yes. Lately, USB 3 stuff is better in that the speeds are approaching
rocket science, so if the manufacturer doesn't get it right, things
rapidly implode. But as far as getting useful error messages and such,
it's almost like the state of networking 20 years ago. You just had to
follow the rules and swap stuff out if it wasn't working. Error codes
might mean something to a developer but they're useless for mortal
users.
Yeah, with storage devices at least it's a bit easier, they just speak a
form of SCSI over the USB interface (even the older mass storage ones),
so if you have some understanding of SCSI, it's not too hard to
translate. Part of the issue though is that USB was designed originally
for input devices, and that has had a significant impact on how it got
designed. Add to that that most USB devices other than input devices
aren't standards compliant in some way (usually it's incomplete
descriptors or not properly negotiating power usage), and it starts to
become rather impressive that things actually work to the degree they do.
I really think USB hubs help fix a lot of USB related problems, even
when it's not a power related problem. Currently I'm using internal
SATA in a NUC for the primary storage, but use send/receive to two
separate raid1 volumes that are USB drives. I can balance/scrub, and
read/write to any and all drives with no problems since getting a
dyconn "industrial" (probably a design term, it's aluminum not
plastic) hub. Before that, one drive or another would just
intermittently reset, usually to no ill effect, but once it wigged
out, vanished, and reappeared as a completely different /dev/sdx
device. The enclosures are crap, the manufacturer (ASMedia Technology
Inc.) didn't bother to fully populate all of the USB descriptors and
it doesn't pass through physical sector size properly, or report max
power correctly, etc.
That's interesting, I've usually had really good results with ASMedia's
USB devices (for reference, they're the semiconductor division of the
same company that ASUS and ASRock are owned by); as far as not passing
through physical sector size properly though, that's normal on almost
all external IDE/SATA adapters (both enclosures and regular adapters),
as is not properly handling commands other than the basic ones needed
for disk access (such as SCT stuff and SMART related commands). That
said, the USB issues on the NUC don't surprise me too much, Intel's USB
controller chips have been known to have hardware bugs (especially their
original XHCI implementation), and I've seen stuff similar to what
you're talking about before with other Intel systems. Now, for other
systems, you have to keep in mind that most of them have hubs internal
to the system, and the external USB ports don't go directly to the USB
controllers, but quite often these hubs are not particularly high
quality, so they often make things worse.
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