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

[Alberto Bursi <alberto.bursi@outlook.it>]

On 01/04/19 00:45, J. Bruce Fields wrote:
> 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.


Afaik quite a few consumer Crucial SSDs do have power loss protection 
(those that advertise it either have a large

bank of capacitors on their PCB or use newer flash that for some reason 
can do without that)

-Alberto