Re: Western Digital Red's SMR and btrfs?

[Alberto Bursi <bobafetthotmail@gmail.com>]

On 12/05/20 00:42, Phil Karn wrote:
> On 5/11/20 14:13, Alberto Bursi wrote:
>>
>> Afaik drive-managed SMR drives (i.e. all drives that disguise
>> themselves as non-SMR) are acting like a SSD, writing in empty "zones"
>> first and then running garbage collection later to consolidate the
>> data. TRIM is used for the same reasons SSDs also use it.
>> This is the way they are working around the performance penalty of
>> SMR, as it's the same limitation NAND flash also has (you can write
>> only a full cell at a time).
>>
>> See here for example
>> https://support-en.wd.com/app/answers/detail/a_id/25185
>>
>> -Alberto
> 
> Right, I understand that (some?) SMR drives support TRIM for the same
> reason that SSDs do (well, a very similar reason). My question was
> whether there'd be any reason for a NON-SMR drive to support TRIM, or if
> TRIM support necessarily implies shingled recording. I didn't know
> shingled recording was in any general purpose 2.5" spinning laptop
> drives like mine, and there's no mention of SMR in the HGST manual.
> 
> Phil
> 
> 
> 


Afaik there is no good reason for a normal hard drive to have TRIM 
support, as normal drives don't need to care about garbage collection, 
they can just overwrite freely.

I would say that TRIM implies either SMR or flash cache of some kind. 
Lack of TRIM isn't a guarantee though, some SMR drives (identified by 
their performance when benchmarked) were not reporting TRIM support.

It seems all three HDD manufacturers (WD, Toshiba and Seagate) just lied 
to everyone about the use of SMR in their drives for years and this was 
only discovered when this went into NAS-oriented drives that 
(unsurprisingly) blew up RAID arrays.

I would not trust the manual or official info from the pre-debacle 
period that much.

-Alberto