Power Outage...

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Power Outage...

Postby justinmburrous » Thu Jun 02, 2011 11:25 pm

Hey guys. last night I had a power outage at my house... I have had others, but this one caused some issues. When the power came back on, my pogoplug (pink) was reset. None of the stuff on the USB stick was there anymore. I did a reinstall of everything and everything is now working, so its not a big deal, but my question is why did this happen?

The reason I ask specifically is because I can unplug my pogoplug, wait for it to restart, and then ssh in with no problems (and everything is still there). Why was this time different do you think?
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Re: Power Outage...

Postby WarheadsSE » Thu Jun 02, 2011 11:43 pm

This time, a write failed at a really bad time. Partition = crapola = data loss.
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Re: Power Outage...

Postby justinmburrous » Fri Jun 03, 2011 4:35 am

Hmmm... Guess that makes sense. I guess I am just used to better error handeling on desktop machines.

No issues when I unplug (which I have done a lot).
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Re: Power Outage...

Postby crimsonredmk » Sun Jun 05, 2011 3:34 am

That's a huge downside to ext2, no journals for records of what was where at what point for quick recovery. But for flash memory it's a must. USB spinning hard disks don't have this on desktops since you're not worrying about writing to a journal every time, since there's no flash memory to wear out. Solution: get a $40 250GB+ USB hard drive, 5400 RPM won't be a bottleneck on ARM.
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Re: Power Outage...

Postby fenschop2 » Thu Jun 30, 2011 7:49 pm

This happened to me several times now, and is quite annoying. I like to have a low power solution, so prefer to use a USB memory device.

I am considering to get a USB drive with a hardware readonly switch. Is there some guide about installing archlinux on a readonly filesystem? Would it be as easy as only mounting /var on a writable device?
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Re: Power Outage...

Postby kmihelich » Thu Jun 30, 2011 8:42 pm

You can just boot to the OS read-only. You just need to take care of logging, and go through any applications you installed and figure out what they might need to write to, and locate that somewhere else.
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Re: Power Outage...

Postby crimsonredmk » Fri Jul 01, 2011 6:07 am

Pogoplug's default firmware does this, you can look in there for ideas and hints I guess. They do a lot of mounting magic to get things right, but you won't have to do as much. /var and /tmp come to mind immediately.
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Re: Power Outage...

Postby hydro » Fri Jul 01, 2011 12:13 pm

mikestaszel wrote:That's a huge downside to ext2, no journals for records of what was where at what point for quick recovery. But for flash memory it's a must. USB spinning hard disks don't have this on desktops since you're not worrying about writing to a journal every time, since there's no flash memory to wear out.

I'm not an expert, but I read that nowadays USB flash drives, just like SSDs, know wear levelling and the journal is not always written to the same place on the drive. Also the Arch Linux Wiki article Installing Arch Linux on a USB key says that "ext4 with a journal should be fine". Finally, journalling increases writes only by a few percent.
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Re: Power Outage...

Postby fenschop2 » Sat Jul 02, 2011 1:07 pm

Also the Arch Linux Wiki article Installing Arch Linux on a USB key says that "ext4 with a journal should be fine".


I think I have read that the problem is that booting the pogoplug can only be done from ext2. Isn't this the case?
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Re: Power Outage...

Postby hydro » Sat Jul 02, 2011 3:50 pm

That's right, but you can create a separate ext2 boot partition for that purpose, see here.
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