David Higton  wrote:
> In message 
>           bob prohaska  wrote:
>
>> Martin Gregorie  wrote:
>> > On Sun, 13 Dec 2020 16:38:29 +0000, bob prohaska wrote:
>> >
>> > > I attribute the acceptable performance to the drive being new, with 1
>> > > TB capacity. Once it starts re-writing old sectors it'll likely slow
>> > > much more.
>> > >
>> > AFAIK trim isn't supposed to do anything useful to a hard drive
>> > regardless of speed or capacity, but I know nothing about SMR, except
>> > that an article I just read says its really only suitable for large
>> > scale  data storage with minimal updating, i.e. not something I'd use
>> > for the  (main? only?) storage volume for a Linux or Windows system and
>> > definitely  not for a journalled fling system.
>> >
>> Practically, SMR is not readily avoidable. It's denser and therefore
>> cheaper than conventional perpendicular recording and has found its way,
>> unbidden, to a wide range of sizes, speeds and brands. The drawback is
>> that, like flash, data is written in relatively large blocks. Writes to an
>> entirely unused  block proceed without a delay. Changes to an
>> already-written block require it be copied, edited and re-written in much
>> the same fashion as flash, absent the write fatigue problems of flash. Trim
>> functions on an SMR drive much as it does on a flash device, preemptively
>> preparing new, empty blocks for prompt use by consolidating partly-used
>> blocks accumulated during earlier writes.
>>
>> When something triggers a long period of sustained writes, like
>> reconstructing a raid array, this overwhelms the preparatory consolidation
>> and slows writes to a crawl. It's not that it doesn't work, rather that it
>> works badly.
>>
>> I should emphasize that this summary is my own interpretation of a random
>> selection of Internet research, and is therefore entirely suspect......
>
> I've drawn the same conclusions as you, from what I've read.  With one
> small exception: I believe that, if you dig deeply enough into the
> manufacturer's specification, you can see whether a particular drive
> uses SMR, and therefore avoid it if you so wish.

Apparently that is a comparatively recent development. There were complaints
that SMR was deployed without warning. In the case of my drive, specs at
https://www.seagate.com/www-content/product-content/seagate-laptop-fam/barracud
a_25/en-us/docs/100807728a.pdf
the drive is advertised as PMR but also supports TRIM. AFAIK there's little
point
in having both. There is also no spec for write speed, only read. The
combination
is at least a little suspicious.

Exactly what's going on is unclear. Certainly, it pays to check first.

Thanks for writing!

bob prohaska

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