Re: simple Chunk allocator like calculation to replace Factor based calculation

[Wang Yugui <wangyugui@e16-tech.com>]

Hi, Qu Wenruo

> On 2020/10/1 下午11:36, Wang Yugui wrote:
> > Hi, Qu Wenruo
> > 
> > Chunk allocator like calculation will get the right value, but it is
> > slow for big file system such as 500T.
> 
> Nope, the ballon allocator doesn't have any size limit, thus it will try
> to use as much space as possible in a single run.
> 
> If the 500T fs only has say 100T used, and the remaining 400T is split
> into, say 2 parts, then just two small run would finish.
> 
> On the other hand, if the 500T is mostly used, only 100T unallocated and
> the 100T is in a big unallocate chunk (under most cases it's true), then
> just one allocation run is enough.
> 
> So in short, it's unrelated to the fs, but how fragmented the
> unallocated space is.
> And normally unallocated space is not fragmented at all, thus it's very
> speedy.

We need some more complex example for 'Chunk allocator like calculation'
to make it easy to understand.

such as
1) RAID10 with 8T,1T,1T,1T,1T
    the virtal chunk size of 1st iteration:	1T or 0.33T?
    1T    chunk will use 4T at most
    0.33T chunk will use 5.33T at most?

2) RAID10 with 8T,1T,1T,1T,0.5T
    the virtal chunk size of 1st iteration:0.5T or smaller?

Best Regards
王玉贵
2020/10/02


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