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Re: New Pi
On 15/05/2014 08:33, Rob wrote:
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But that all assumes its a simple storage system like a hard disc where  
once data has been written, it stays put. So the worse that can happen  
is a partial write and the journal information will indicate what the  
last consistent state was to recover to.

With all but the simplest flash storage performing wear levelling, there  
is an extra level of mapping between the storage the journalled filing  
system things there is, and the actual flash memory blocks. If the flash  
controller is changing this mapping when the power goes, the data will  
still be there, but in a completely scrambled order that journalling  
can't recover from.

---druck

Re: New Pi
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Hmm that is bad.  I would have expected flash controllers to do the
remapping operation in such a way that it would not corrupt the storage
when it is interrupted halfway.

(i.e. first erase an area, then copy the data that has to be there,
and only then change the pointer table to indicate that the data at that
blocknumber is to be found at the new location, and free the original
location)

Re: New Pi
On 15/05/14 13:45, Rob wrote:
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supercapacitiors and intelligence in the card may in time solve that.

weird things happen when power goes up and down though.

I have no idea how modern computers work, but we used to actually build  
stuff into cicuitry so that if the supply rails was lower than a certain  
capacitor, that meant power had gone and you would then had few clock  
cycles to set an interrupt going to at least preserve the most important  
stuff.

'watchdog' in my day meant a series of JMP RESET instructions inserted  
into random places between code blocks in ROM so that in the event of  
the instruction pointer having been corrupted (typically by a nearby  
nuclear EMP pulse) the system would at least reboot into some semblance  
of  where it was....we used static ram too, for similar reasons.

Software cannot be guaranteed to work when a register or memory cell  
changes under your feet..




--  
Ineptocracy

(in-ep-toc?-ra-cy) ? a system of government where the least capable to  
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Re: New Pi
On 15/05/14 08:33, Rob wrote:
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yep. Its the one that doesn't that gets you

we had a server. SCO unix actually. For years when the power went down  
it came back up, grumbling, but it came.

ALL the company data and years of bits of source code were on it.

A lot of it was backed up, but not all. It grew to have many disks  
inside it.

At leasts two I think. Maybe more.

Then we had a powercut. It went down. Then the power came on for 5  
seconds as it was rebooting. Then the power went again.

That finished it. The boot disk was totally unrecoverable. IT didnt even  
have recognisable partitions on it.

The big company data was on the second drive however and that was OK, so  
we didn't lose all of it.

I stopped autobooting servers on power on after that.

99 times out of a hundred on a system tat isn't busy, pulling the power  
wont cause irreparable damage. But if the system IS busy around the boot  
sector you can utterly destroy it.

whether we had a head crash, or a random write to a sector I will never  
know.


--  
Ineptocracy

(in-ep-toc?-ra-cy) ? a system of government where the least capable to  
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Re: New Pi
On Thu, 15 May 2014 13:49:05 +0100, The Natural Philosopher wrote:

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Not on a UPS then? And if the UPS has shutdown as well doesn't start
up again until it has recharged its batteries enough to maintain
power long enough for conected kit to cleanly shutdown (again).

--  
Cheers
Dave.




Re: New Pi
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My experience with UPSes has not been that good...
Maybe they are better today, but the ones I used were usually not
too clever.  For example, when the power drops and it detects it has
a certain number of minutes left, it shuts down the systems (or better:
the systems shutdown themselves after receiving an indication from the UPS)
and then when the power returns before the time actually runs out, the
UPS goes back to online mode and the systems are and remain OFF.
Of course, once it has given the indication that shutdown should be
done it should always cycle the power even when the input mains is back.

Others could not be turned on when the batteries are charged but no
input is available.  So you can put them online and they will take over
when power drops, but you cannot get one fully charged out of storage
and use it to power some equipment during a blackout.  And it even is
inconvenient to use one to vacuum your car interior.
(you need to plug it in and switch it on in the house, then carry it
to the car while it is running)

Furthermore, the MTBF of a typical UPS is shorter than that of the mains
itself, over here.  But that varies a lot depending on location.

Re: New Pi
On 15 May 2014 16:04:12 GMT, Rob wrote:

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TBH I'm not overly enamoured either but the small UPS I have is
mainly there to maintain the phone system (two VOIP lines over ADSL).

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'tis true but if there is no one here to press the servers power
button it's no great problem.

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That sort of depends on how you have your systems set up. Do you keep
things powered until the battery is almost exhausted then shutdown or
do you shutdown say 2 mins after the power has gone thus load
shedding and keeping battery for "essential" low power kit? I do the
latter.  

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Mine will "cold start".

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A guesstimated average would be about 1 or 2 outages a year here. But
that can be anything from an auto recloser cycle (off for a couple
seconds) to 36+ hours (ice storm bringing down lines and snapping
poles).

The UPS will keep the phone system running for about 6 hours, if the
outage is going to be much longer than that I'll be dragging the
genset out of the garage to power the heating system, fridges and
freezers etc

--  
Cheers
Dave.




Re: New Pi
On Fri, 16 May 2014 09:05:43 +0100 (BST)

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A half-way decent one using lead-acid 'float' type batteries should do a *lot*
better than that. At work we have one that is over 10 years old, with it's
original batteries. We're in converted farm buildings so have frequent outages.
Some short, some stuttery some hours. It's an on-line type so there is never a
dip until it eventually shuts down (if everything is left on that long).

--  
W J G

Re: New Pi
On 15/05/14 14:46, Dave Liquorice wrote:
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WE weren't in them days.

I dont use it now either.

Home server only with mirror disks. Chances are one will make it.



--  
Ineptocracy

(in-ep-toc?-ra-cy) ? a system of government where the least capable to  
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Re: New Pi
On Thu, 15 May 2014 17:33:14 +0100, The Natural Philosopher wrote:

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All the same, with all the dire warnings about power cuts from 2015  
onward thanks to a lack of gummint and powerco spending on replacement  
generating kit I'm seriously considering getting a small UPS that can at  
least keep my main box alive long enough for it to do a clean shutdown.  
An automatic restart when the power comes back would be nice but not  
essential.


--  
martin@   | Martin Gregorie
gregorie. | Essex, UK
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Re: New Pi
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However some (most/all) disks were found to be lying when the OS performed
the fsync() and asked the drive for write conformation and still had
data in their on-board RAM cache un-written to disk. This was driven
by marketing to make it look like they were running faster than they
really were. Not sure if this applies to SD cards though, but given the
relatively slower speed of writing, it would not surprise me.

Have a read through: http://brad.livejournal.com/2116715.html

Gordon

Re: New Pi
On Thu, 15 May 2014 11:14:28 +0000, Gordon Henderson wrote:

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Icky, but that was written 9 years ago. Have things moved on since and,  
if so, in which direction?


--  
martin@   | Martin Gregorie
gregorie. | Essex, UK
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Re: New Pi

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I have tried the apt-get line which proceeded OK until it displayed on  
screen 0%[ connecting to Debian] when the system seemed to freeze.

No download and I had to reboot.

What is wrong?

Malcolm


--  
T M Smith
Using an Iyonix and RISC OS 5.20 in the North Riding of Yorkshire

Re: New Pi


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Is it plugged into a WIRED network ?
"connecting to Debian" really means that is is trying to get out on the int
ernet. Is it possible?

Does ping 8.8.8.8 give you a reply? (8.8.8.8 is Google's name server)






Re: New Pi



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 Thanks for that! :-)

 I knew it would be worth lurking in this NG even though it's unlikely
I'd actually buy myself a Pi. You can pick up a lot of useful hints
and tips from this NG and that ping test is a nice easy one to
remember. I've just tried it on this win2k box and got an average ping
time of 20ms.
--  
Regards, J B Good

Re: New Pi

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Well, hmm, yes, but I meant you to ping from the Pi.  
To see if you have networking from the pi,
since it is the pi that will contact debian's repository
when doing apt-get update
--


Re: New Pi



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 Yes, I did understand that point. I was just chipping in to thank you
for providing an easy to remember ping address, usable on_any_ system
with a CLI and internet access.
--  
Regards, J B Good

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