How Reduce Disk read write overhead?

Question

I have one website mainly composed on javascript. I hosted it on IIS. This website request for the images from the particular folder on hard disk and display them to end user. The request of image are very frequent and fast.

Is there any way to reduce this overhead of disk read operation ?

I heard about memory mapping, where portion of hard disk can be mapped and it will be used as the primary memory. Can somebody tell me if I am wrong or right, if I am right what are steps to do this. If I am wrong , is there any other solution for this ?

Answer 1

While memory mapping is viable idea, I would suggest using memcached. It runs as a distinct process, permits horizontal scaling and is tried and tested and in active deployment at some of the most demanding website. A well implemented memcached server can reduce disk access significantly.

It also has bindings for many languages including those over the internet. I assume you want a solution for Java (Your most tags relate to that language). Read this article for installation and other admin tasks. It also has code samples (for Java) that you can start of with.

In pseudocode terms, what you need to do, when you receive a request for, lets say, Moon.jpeg is:

String key = md5_hash(Moon.jpeg); /* Or some other key generation mechanism */
IF key IN memcached
   SUPPLY FROM memcached /* No disk access */
ELSE
   READ Moon.jpeg FROM DISK
   STORE IN memcached ASSOCIATED WITH key
   SUPPLY
END

This is a very crude algorithm, you can read more about cache algorithms in this Wiki article.

Answer 2

The wrong direction. You want to reduce IO to slow disks (relative). You would want to have the files mapped in physical memory. In simple scenarios the OS will handle this automagically with file cache. You may look if Windows provides any tunable parameters or at least see what perf metric you can gather.

If I remember correctly (years ago) IIS handle static files very efficiently due a kernel routing driver linked to IIS, but only if it doesnt pass through further ISAPI filters etc.. You can probably find some info related to this on Channel9 etc..

Long term wise you should look to move static assets to a CDN such as CloudFront etc..

Like any problem though... are you sure you have a problem?