UNIX for Dummies Questions & Answers

hi,

1) is logical partition the same as physical partition except that one is physical and the other is logical?

2) then it must a one to one ratio?

I would assume that a physical partition is like a primary partition (which you are very limited on the number you can have) and a logical partition is a partition within an extended partition. Although you may only have one extended partition it can contain many logical partitions...

clear as mud ?

With physical partitions, a disk is subdivided into partitions. And somehow the disk driver knows about the subdivision scheme. The driver may read a table off the first sector of the disk. Or the driver may just get the model number of the drive and pick a built-in table. The special files are named to indicate the section. c0t0d0s2 would be section "2" of the disk (which was always the whole thing).

With logical volumes, a disk like c0t0d0s2 (or maybe just c0t0d0 theses days) is just a physical volume which gets tossed into a pool called a volume group. Then you have very great flexibility in creating logical volumes. A logical volume may be a very small slice of a disk. Or it may be so large that it is several disk drives.

You might think of it like this:

Your house has lots of closets for storage. They are small and shattered out in many rooms. Many closets are full and you have trouble finding things. It would be great to have a magical 'master door' that allows you to put things in the 'master door' and, by magic, your things are automatically placed in the closets in an organized way. PLUS, when you want to get something out of your closets, you simply ask the 'master door keeper' to get the item and they find it for you and keep the closets clean and neat.

Logical volumes and logical volume managers provide this kind of service for disk partitions (closets) and data (stuff you put in closets).