Re: [gentoo-user] Gparted leaves gaps

[Michael]

On Thursday, 1 April 2021 16:06:37 BST Peter Humphrey wrote:
> On Thursday, 1 April 2021 11:13:07 BST Michael wrote:
> > You could check/set the alignment of logical-physical sectors yourself, by
> > making sure the start of your partitions is divisible by 8, instead of
> > adopting the GParted 1MB default boundary in any cases where it is not
> > necessary.
>
> So it seems to be the partition start points that matter; sizes have nothing
> to do with it. Makes sense, now I think about it.

Yes, it is the starting point which determines the first 512 byte logical 
sector and those what follow it, are aligned with the first 4096 byte physical 
sector and those that follow it.

When these are not aligned a write operation instructed by software could 
straddle more than one physical sector, even when the data to be stored is 
less than 4096B.  This results in moving, deleting, writing more sectors and 
data than necessary, a measurably inefficient process.  This is noticeable on 
spinning drive benchmarks and can get much worse on flash and SSDs with their 
coarser erase Vs write pages (a.k.a. write amplification).


> I've just realigned all my partitions to accord with that insight. It turned
> out that most of them had small differences from 8^n sizes and start
> points, which would explain all those unpartitioned spaces.
>
> All well now. Thanks all.

I recall fighting against gparted's optimal alignment myself when partitioning 
tools first started catering for 4K size sectors, only having to realign my 
partitions as soon as I realised the error of my ways!  ;-)