MySQL - Where can I find metrics on the performance of Blob vs file system?
The main cost of handling the data is the I/O.  You are doing approximately the same amount of I/O, whether it is in 4KB chunks in the OS (plus directory traversal) or 16KB chunks in InnoDB (plus indirect block lookup).

The filesystem and InnoDB are cached in radically different ways; this may factor into a difference -- depending on how cacheable the blogs are.

You say "rarely retrieved". So why does speed matter?

So, I doubt if it will be more than 25% difference.  And I can't predict which will be faster.

As for space, again there are several differences, so it is hard to predict which would be tighter.  In any case, the diff can't be more than about 2% for the size blobs you mentioned.

How compressible are the blobs?  (Most image formats are already compressed; text is typically compressible 3:1.)  If compressible, then do so in the client.  (InnoDB's builtin optional compression is easier, but not as good.)

And, yes, having it in a "parallel table" (as you mentioned) is often better.

Another point -- If the blob is an image destined for a web page, it is more efficient to simply have it in a file and say &lt;img srg=file-path&gt;.  If it is in a table BLOB, you have to do extra work to hand it off to the web page.  Since I/O is the main difference, I might expect the img tag to be 2x faster.