choice of external USB drive for mount at boot

Have you considered hacking a USB cable? Leave alone the White (data -) #2 and Green (data +) #3 wire in the cable to connect data unaltered, and break out the Red (+5VDC) #1 and Black (Ground) #4 wires cut and split so the Pi side is isolated and the drive side is connected to a wall wart mains adapter of sufficient Amperage to prevent back-powering the Pi.
Does the drive have to be new? A used .5TB Buffalo USB drive on EBay may also satisfy your requirements.
-(o=8> wiz.
--
  All ladders in the Temple of the Forbidden Eye have thirteen steps. 
There are thirteen steps to the gallows, firing squad or any execution. 
 Click to see the full signature
Reply to
DisneyWizard the Fantasmic!
Loading thread data ...
Only cut the red wire. Do not cut the black wire as you still need a ground connection. The black wire should be split and connected to the PSU, disk and the Pi.
Reply to
Dom
It's an interesting idea but (for this home server project, anyway --- I'll bear this in mind for later tinkering) I think I'll pay a bit more for reliability instead of splicing stuff together myself!
--
Why is it drug addicts and computer afficionados are both  
called users?                          --- Clifford Stoll
Reply to
Adam Funk
That's a good point. I've personally come across two kinds of HDD enclosures/adapters: the "full" enclosure (box that you put the SATA/IDE drive inside of, with a USB cable & an external power supply); and the "slide-in" kind. I've only used them for recovering data from drives from machines that had something else wrong with them, & the full-box types I've seen looked quite cheap (the one I bought was in fact quite cheap too).
--
Our scientific power has outrun our spiritual power. We have guided 
missiles and misguided men.             --- Martin Luther King, Jr.
Reply to
Adam Funk
Wow, how can two models (7200.11 & 7200.14) be so outstandingly worse than all the others --- especially when others from the same brand aren't outstandingly bad?
Reply to
Adam Funk
Sorry if this is a stupid question, but what good does it do me to know (after buying a reputable product) what the physical drive is inside the package?
--
You measure democracy by the freedom it gives its dissidents,  
not the freedom it gives its assimilated conformists.  
 Click to see the full signature
Reply to
Adam Funk
On the other hand, splicing it yourself could expose a potential unreliability issue - some USB cables have ridiculously thin wires, and this produces voltage fluctuations. Cutting and splicing one would show you the problem, and allow you to replace the cable with a better one.
--
Alan Adams, from Northamptonshire 
alan@adamshome.org.uk 
 Click to see the full signature
Reply to
Alan Adams
I guess we should shop for USB cables by weight per unit of length? ;-)
--
XML is like violence: if it doesn't solve the problem, 
use more.
Reply to
Adam Funk
Certainly not. WD Red series is the drive made for 4-bay NAS enclosures marketed to the SMB/SOHO segment. They aren't very fast, but supposedly tuned to not be so bad with wobble from neighbors, or ignore slower SATA bus timeouts that seem to happen more often with those sort of devices.
I don't know what segment of datacenter you'd be in, but WD's "datacenter" drives are the RE's. (ie. RAID Enhanced). I guess they've expanded out recently with Se and Ae as well. Still pretty poor RPMs and throughput for a datacenter drive, I'd say they barely play in that space. (with only on SAS 7200RPM drive available), where commonly we'd use 10k RPM SAS and 15k RPM SAS.
Very easily. Either the technology used to make those models can't stand up to normal operations (ie. can Hitachi Helium drives actually keep their Helium inside and working over a 5-10 year lifespan?), or they were made all in the same plant, that consistantly got bad parts, or some failed process on that line. Ie. a specific plant probably makes all of a specific model, as they have to retool for another model, and if they have multiple plants, they'll spread out their production and save on the cost of retooling and downtime while that happens.
Also, there were rumors that after the flooding in Thailand, that affected many drive makers' plants there, that Seagate mostly just stood theirs up again and kept going with all the stock and tools that were flooded and potentially pitted away or damaged by the sea water.
--
Doug McIntyre 
doug@themcintyres.us
Reply to
Doug McIntyre
get
cable to connect data unaltered, and break out the Red (+5VDC) #1 and Black (Ground) #4 wires cut and split so the Pi side is isolated and the drive side is connected to a wall wart mains adapter of sufficient Amperage to prevent back-powering the Pi.
True that, Dom. I had forgotten the device should never ground the shielding, only the host. Oh well, so much for preventing back-powering the Pi AND avoiding a ground loop. So it's back to the powered hub or locating a desktop separately powered hard drive. ?(o=8> wiz.
--
 ? better to learn by mistakes of others, ? Wiz. 
 ?  erroneous examples as provided, ? Wiz. 
 Click to see the full signature
Reply to
DisneyWizard the Fantasmic!
Interesting point! Anyway, I've decided to go down the desktop drive with external power for this, probably a WD My Book --- unless anyone wants to advise against that.
--
To live without killing is a thought which could electrify the world, 
if men were only capable of staying awake long enough to let the idea 
 Click to see the full signature
Reply to
Adam Funk
Interesting, thanks.
--
With the breakdown of the medieval system, the gods of chaos, lunacy, 
and bad taste gained ascendancy. 
 Click to see the full signature
Reply to
Adam Funk
I just discovered last night that my powered hub will back power the Pi. We had a nearby lightning strike and everything seemed to have gone wonky. The lights on the Pi were out (other than the power) so I pulled the power cord. The power light didn't go out... I had to pull the hub power cord as well.
I've taking the hub apart, so I knew the hub had nothing to prevent back powering. I guess I just assumed the Pi would prevent that, but once I thought about it I realize with the crude power distribution on the original Pi, it was unlikely. Anyone know if you can back power a B+ or a Pi 2?
--

Rick
Reply to
rickman
You can't boot them by using only back power through the USB. The USB current control circuits prevents it. You need to power via the normal microUSB/GPIO pins/power test points.
However, once the B+/2 has booted up and the USB power circuit has been enabled, the main power source can be removed and the Pi will continue to run on back power.
Reply to
Dom
I think that sucks. There should be circuitry to disable back powering. I would have expected this to be required of the USB hubs as well.
--

Rick
Reply to
rickman
As with everything on the Pi, that comes down to costs - both development and production. Be glad that the newer Pis have better power regulation and at least some USB power control, unlike the originals.
USB hubs aren't supposed to back power. Many do. Again this mainly comes down to costs.
Reply to
Dom
On Thu, 18 Jun 2015 11:16:30 +0100, Adam Funk , in
I have a couple of 2TB WD externals that have held up pretty well -- several years of use. No complaints.
--
Consulting Minister for Consultants, DNRC 
I can please only one person per day. Today is not your day. Tomorrow 
 Click to see the full signature
Reply to
I R A Darth Aggie
Thanks.
--
Nam Sibbyllam quidem Cumis ego ipse oculis meis vidi in ampulla  
pendere, et cum illi pueri dicerent: beable beable beable; respondebat  
 Click to see the full signature
Reply to
Adam Funk
You can then look up the spec/reviews and see if what the makers, reputable or not, have fitted is considered a "decent" or a cheap, slow, unreliable drive.
--
Cheers 
Dave.
Reply to
Dave Liquorice
the
and
...
Why? Unless I'm mistaken the data bus is balanced, bi-directional, half duplex, at least for USB 1 & 2. Just adds another balanced pair to enable full duplex. What ever, no ground is required for a balanced circuit to work.
I'd keep the screen intact which may or may not connect the grouds of each device. Screen to chassis/ground at the host end and floating at the remote end appears to be normal and makes sense.
--
Cheers 
Dave.
Reply to
Dave Liquorice

ElectronDepot website is not affiliated with any of the manufacturers or service providers discussed here. All logos and trade names are the property of their respective owners.