topic Re: Difference between block and file i/o in Operating System - HP-UX

Difference between block and file i/o

Gourab Baksi — Tue, 19 Jun 2007 07:51:57 GMT

What is the difference between block i/o (as in case of a SAN device) and file i/o (as in case of a NAS device)?

Why is block i/o faster than file i/o?

Re: Difference between block and file i/o

Court Campbell — Tue, 19 Jun 2007 09:31:10 GMT

I think your answer lies more in the differences between a SAN and a NAS. A san is like having a drive or tape inside of a physical machine. A NAS in the other hand is like connecting to a server via NFS, or FTP, or CIFS, etc. That is why you would notice a i/o difference.

You might look into taking this online class:

http://education.itresourcecenter.hp.com/TrainerII/en_US/catalog/catalogDetail.jsp?id=prod1280004

It's free. It tells more specifics on the difference between a SAN, NAS, and DAS.

Re: Difference between block and file i/o

A. Clay Stephenson — Tue, 19 Jun 2007 09:50:37 GMT

This is really an "all sqauares are rectangles question" in that all "cooked" file i/o is built on top of block i/o. Block i/o means that transfers to and from disk are done in chunks rather than individual bytes AND that the UNIX buffer cache is used to minimize physical i/o.

The primary difference between these two is that under block i/o there is no concept of files, filesystems, or directories. The entire disk or LUN is simply a big bunch of disk blocks. Under file (cooked) i/o, this big bunch of disk blocks is divided into small chunks that are logically connected to form files and directories.

Re: Difference between block and file i/o

Gourab Baksi — Mon, 25 Jun 2007 03:19:56 GMT

I guess that answers what I wanted to know..
Thanks :)