How to store images in your filesystem

Just split your userid from behind. e.g.

UserID = 6435624 Path = /images/24/56/6435624

As for the backup you could use MySQL Replication and backup the slave database to avoid problems (e.g. locks) while backuping.

one thing about distributing the filenames into different directories, if you consider splitting your md5 filenames into different subdirectories (which is generally a good idea), I would suggest keeping the complete hash as filename and duplicate the first few chars as directory names. This way you will make it easier to identify files e.g. when you have to move directories.

e.g.

abcdefgh.jpg -> a/ab/abc/abcdefgh.jpg

if your filenames are not evenly distributed (not a hash), try to choose a splitting method that gets an even distribution, e.g. the last characters if it is an incrementing user-id

I'm using this strategy given a unique picture ID

• reverse the string
• zerofill it with leading zero if there's an odd number of digits
• chunk the string into two-digits substrings

• build the path as below

  17 >> 71 >> /71.jpg163 >> 0361 >> /03/61.jpg6978 >> 8796 >> /87/96.jpg    1687941 >> 01497861 >> /01/49/78/61.jpg

This method ensures that each folder contains up to 100 pictures and 100 sub-folders and the load is evenly distributed between the left-most folders.

Moreover, you just need the ID of the picture to reach the file, no need to read picture table containing other metadata.User data are not stored close together indeed and the ID-Path relation is predictable, it depends on your needs.