I hope someone will correct me if I'm wrong but this is what I think:

the @ sign is just telling you "at what protection level".

the "@ 5/4" is referring to the 4+1 data protection you have. The parity would be an extra 25% of the total file (an extra 1 parity stripe for 4 data stripes).

For the metatdata the "@ 2x" refers to  2x mirroring. Remember ALL metadata is mirrored and since metadata in itself is considered overhead, all of it is calculated as such.

So if you look @ it (see what i did there?)  like this, the mirrored metadata from above is equal to 1mb and 25% of the 1 mb file that will represent the overhead is the .251 of the file.

I hope this helps!

you got it right on. Note that 1mb is actually equal to 1024kb and that DOES equal out to 8 units exactly.

it would end up being 8 data stripes and 2 parity stripes for a total of 10.

Thanks

For your answer

To clarify one point, there are only 2 stripes, or protection groups, in this example.  The 128kB data chunks are referred to as stripe units, so the four data and one parity stripe unit make up a stripe of 512kB + 128kB. 

With that picture

I understand the stripe unit

Thanks