Re: Is it possible that certain physical disk doesn't implement flush correctly?

[bfields@fieldses.org (J. Bruce Fields)]

On Sat, Mar 30, 2019 at 09:24:37PM +0800, Qu Wenruo wrote:
> 
> 
> On 2019/3/30 下午9:14, Supercilious Dude wrote:
> > On Sat, 30 Mar 2019 at 13:09, Qu Wenruo <quwenruo.btrfs@gmx.com> wrote:
> >>
> >> If controller is doing so, it must have its own power or at least finish
> >> flush when controller writes to its fast cache.
> >>
> > 
> > The controller has its own battery backup to power the DRAM cache, as
> > well as flash storage to dump it onto in the exceedingly unlikely
> > event that the battery gets depleted.
> > 
> >> For cache case, if we have enough data, we could still find some clue on
> >> the flush execution time.
> >>
> >> Despite that, for that enterprise level usage, it's OK.
> >>
> >> But for consumer level storage, I'm not sure, especially for HDDs, and
> >> maybe NVMe devices.
> >>
> > 
> > How do you distinguish who is a who? Am I an enterprise or a consumer?
> 
> Easy, price. :P
> 
> To be honest, I don't really care about that fancy use case.
> It's the vendor doing its work, and if something wrong happened,
> customer will yell at them.
> 
> I'm more interesting in the consumer level situation.

The feature seems to be advertised as "power loss protection" or
"enhanced power loss data protection".  Which makes it sound like a data
safety feature when really it's a performance feature.  E.g. these are
the Intel drives with "EPLDP":

	https://ark.intel.com/content/www/us/en/ark/search/featurefilter.html?productType=35125&0_EPLDP=True

Last I checked there were some that weren't too expensive.

--b.