My current limit for profitability is ~ US$5.10 per Ghps.
Any more than this and you're unlikely to make a complete ROI in the first 3 months - and if you have to bank on mining more than 3 months to make a complete ROI then you can't make any good (reliable) estimates anyway.
That's a pretty reasonable number. Bitmain comes close. Bitfury is double that. Disappointingly overpriced.
I think bitmain is right on the nose with thier pricing 90% of the time. the current 1.45BTC batch and the 2.65BTC batch they had 2 weeks ago both fall a little norht of what i consider 'reasonable'. 0.0065BTC/GH seems like a fair number to me for an antminer (2w/GH) and maybe 0.0075BTC/GH for a bitfury due to the slightly better efficiency.
however, the difference in user experience is vast. the antminers dont destroy SD cards. My bitfury has been stable for almost 2 weeks, but I am terrified to change it over to a less-noisy PSU for fear that the SD card will need to be formatted and imaged all over again just to get it running, not to mention re-doing all the autotune
Can't you copy the autotune file to a USB stick? "sudo shutdown -h now" has been sparing me reimaging.
on at least 3 occasions 'sudo shutdown -h now' has messed up the SD card image. in contrast when i first had the system i must have safely turned off and on the PSU to do tweaks and pencil mods a dozen times before the first issue with an SD card. At this point i just avoid touching it for fear of it losing my settings.
how could i copy the settings (or better yet, the full image) over the network or onto a usb stick to make backup SD cards?
What SD card are you using. This problem has yet to happen to me, so I'm not sure why people are getting these sd card corruption issues. I think a lot of the kits came with Transcend 4GB or 8GB SD cards and two of my rigs use those, and once again they have yet to give me any file system corruption issues. What I do is I first stop the miner (to prevent it from constantly trying to write to the .stats.log and other files) and then I do a "shutdown -h now". I then wait for all the light on the RaspPi to stop blinking (indicating that the shutdown process is complete) and then and only then I power off the rig. Maybe it's my method maybe it's luck; I dunno.
Regarding the tuning issue, yes I have that too. Because I overclock my rigs after some time (strange effect if you ask me) the overclock increases with age and I find myself having to downclock the chips a bit selectively to maintain stability. Suffice it to say this is a maintenance headache that I'd like to avoid, but with bitfury rigs it's a necessity. In the future I think I will buy only low maintenance miners. Sometimes playing around with this stuff is fun, but at other times I think of all the other more fun things I could be doing with my time.
To make a backup of the system you'd have to take it out of action, put it in a linux or windows box and use a disk image copy program to create some ISO or standard image file of it. In linux you can use the "dd" command. To copy just the key miner settings file you can use plain old ftp or something more fancy like rsync - oh, or NFS.
Heatsinks still haven't arrived, but my first boards ran OK without heatsinks for a couple of weeks or so with no ill effect (and with less-optimal airflow over them), so I suspect I'll plug 'em in now and add the heatsinks whenever they arrive.
