Subject: Re: Capacitors, etc.,
 in hard drives and SSD for DBMS machines...
To: pgsql-performance@postgresql.org
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From: Jean-David Beyer <jeandavid8@verizon.net>
Organization: Institute for Regimented Whimsey
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Date: Fri, 08 Jul 2016 10:56:41 -0400
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On 07/08/2016 07:44 AM, vincent wrote:
> 
> 
> Op 7/8/2016 om 12:23 PM schreef Jean-David Beyer:
>> Why all this concern about how long a disk (or SSD) drive can stay up
>> after a power failure?
>>
>> It seems to me that anyone interested in maintaining an important
>> database would have suitable backup power on their entire systems,
>> including the disk drives, so they could coast over any power loss.
>>
> As others have mentioned; *any* link in the power line can fail, from
> the building's power
> to the plug literaly falling out of the harddisk itself. Using multiple
> power sources,
> UPS, BBU etc reduce the risk, but the internal capacitors of an SSD are
> the only thing
> that will *always* provide power to the disk, no matter what caused the
> power to fail.
> 
> It's like having a small UPS in the disk itself, with near-zero chance
> of failure.
> 
> 
Thank you for all the responses.

The only time I had a power supply fail in a computer was in a 10 year
old computer. When storm Sandy came by, the power went out and the
computer had plenty of time to do a controlled shutdown.

But when the power was restored about a week later, the power flipped on
and off at just the right rate to fry the power supply, before the
system even started up enough to shut down again. So I lost no data. All
I had to do is buy a new computer and restore from the backup tape.

Of course, those capacitors in the disk itself could fail. Fortunately,
there have been giant improvements in capacitor manufacture reliability
since I had to study reliability of large electronic systems for a
military contract way back then.

-- 
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  /V\  PGP-Key:166D840A 0C610C8B Registered Machine  1935521.
 /( )\ Shrewsbury, New Jersey    http://linuxcounter.net
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