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From: =?UTF-8?Q?Bj=C3=B6rn_Lundin?= <bnl@nowhere.com>
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Subject: Re: Move bookworm system from SSD to NVME
Date: Sat, 3 Aug 2024 13:52:39 +0200
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On 2024-08-03 12:07, The Natural Philosopher wrote:

> I am on the edge of my comfort patch here.
> If I were building an SSD I would have a diode and a large capacitor 
> inside it to make sure all its caches were dumped to NVRAM before the 
> voltage collapsed completely.
> 
> But on a big unit this could take a bit of time.
> 
> What happens between a SATA/USB plug and the actual NVRAM is a bit of a 
> mystery.
> 
> We know its nothing like a 1:1 correlation between 'sector' and physical 
> RAM location.
> We knows that physical RAM locations are regularly shuffled for 'wear 
> levelling'
> When is all this done?
> What happens if, during it, there is power failure?
> 
> I honestly do not know, hence the warning to leave the SSD for a few 
> seconds before yanking any power cords
> 
> It can do no harm

And that is my point. sync will do no harm either,
but it might save you, especially when you are dd()ing an image smaller 
that the RAM of the computer.
Like I have 32 Gb RAM, and dd an image of 4 Gb (like a headless) onto a 
SD-card to run an old pi. The interface is slow, yet dd reports done 
within a minute. sync takes a long time to flush it over.

Just waiting a few secs will end in disappointment

-- 
/Björn