:: Re: [DNG] noatime by default
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Autore: Didier Kryn
Data:  
To: dng
Oggetto: Re: [DNG] noatime by default
Le 28/08/2017 à 22:10, Alessandro Selli a écrit :
> On Mon, 28 Aug 2017 at 12:58:24 +0200
> Narcis Garcia <informatica@???> wrote:
>
>> El 28/08/17 a les 11:59, Alessandro Selli ha escrit:
>>> On Sun, 27 Aug 2017 at 17:18:28 -0500
>>> d_pridge <d_pridge@???> wrote:
>>>
>>>> Doesn't this affect the expected lifetime for an SSD?
>>>    Little.  AFAIK this used to be a more serious concern on the first
>>> generation of SSDs, because they suffered strongly from write-wear and
>>> because firmware, drivers and filesystems did not support write-levelling.
>>> Today this is much less of a concern.  SSD cells can stand many more write
>>> operations before wearing (not so so called 3D SSD units, however) and
>>> unit's firmware today apply algorithms to write operations that attempt
>>> to spread writes as evenly as possible to cells avoiding impinging too
>>> many times on the same ones.  Which means that, even if you're writing
>>> several times on the same filesystem's blocks (e.g., the FS's log on a
>>> journalled FS), these blocks are mapped to cells spread here and there on
>>> the SSD that are generally different from write operation to another,
>>> transparently to the filesystem's driver and block allocator.  Plus,
>>> SSD-aware filesystems (designed, among other things, to reduce the impact
>>> of write amplification of cells being rewritten) further help prolonging
>>> the unit's life, regardless of how it is used.

>>>
>> "SSD-aware filesystems" are flesystems mounted with no atime
>    They do more than that:

>
> https://en.wikipedia.org/wiki/Flash_file_system
>

     JFFS2 and the other filesystems, mentionned in this link are for 
raw flash memory, not for the flash-based disk drives (aka SSD) which 
come with a SATA interface and emulate a rotating disk. You cannot put a 
JFFS2 filesystem on an SSD.


     The last implement wear levelling etc in the firmware, so that they 
can be used with the same filesystems you use on a traditionnal disk. 
But, as was said, it is better if the filesystem is aware of the storage 
being on flash.


     Didier