Efficient Blobbing?

I am dealing with blobs up to - I estimate - about 100 kilo bytes in
size.

Storage engine: InnoDB

Frontend: PHP

Some questions:

* I've read somewhere that it's not good to update blobs, because it
leads to reallocation, thus fragmentation, thus bad performance. Is
that true? Any reference on this?

* Initially the blobs get constructed by appending data chunks. Each
chunk is up to 16 kilo bytes in size. Is it more efficient to use a
separate chunk table instead, for example with fields as below?

parent_id, position, chunk

Then, to get the entire blob, one would do something like:

SELECT GROUP_CONCAT(chunk ORDER BY position) FROM chunks WHERE
parent_id = 187

The result would be used in a PHP script.

* Is there any difference between the types of blobs, aside from the
size needed for meta data, which should be negligible.

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