How to set up QA_BLOBS_DIRECTORY correctly?

Question

I'm moving images stored in database to a directory. I created a folder named "blob" inside of my installation folder and change its permissions to 777.

However, I got the error message

The directory /blob/ defined as QA_BLOBS_DIRECTORY is not writable by the web server.

Here's what in the configure file

define('QA_BLOBS_DIRECTORY', '/blob/');

How do I set up in a correct way?

Comments

How about this?
define('QA_BLOBS_DIRECTORY', '/my-installation-folder/blob/');

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You have to give the full path of your installation.Like: /home/yoursite/public_html/installation-folder(if exists)/blobs/