fallocate support ...

[Daniel Phillips]

Hi Lars,

On 03/21/2017 12:37 AM, Lars Segerlund wrote:
>
>  Hi guys,
>
>  I am doing some apps that preallocates files at known locations on 
> disk, continous and the order ( placement ) is important, so I thought 
> I¨d ask if there has been any thoughts about this on tux3 ?
>
>  It¨s really a killer app for streaming, since files at the end of the 
> disk is slower, and files on the outer part of the platter is faster.

Ah, interesting I did not realize that a factor of something less than 
two is so critical. And I guess you are telling us, spinning disks are 
not dead yet.

Yes, this is something Hirofumi and I have discussed in the past. Tux3 
is, in general, well suited to it. It would be required for any kind of 
real-time guarantee. We should have a specific plan for it, and see how 
the current code might be adapted for it.
>  Preferably I¨d like to have continous files of a given size take up 
> as much of the disk as I specify, from outer cylinders to the middle. 
> ext4 has some support to set this up at filesystem creation time 
> through a custom config to mkfs.
>
> So there are two issues, one is large continous file allocation, and 
> the second is file placement.
>
>  Any thoughts ?
>
What API do you propose, for the user to specify these constraints?

Regards,

Daniel