Basic concepts of LUN, RAID, volume...
Could somebody please describe how the concepts of LUN, RAID, and volume relate to each other? Individually, I know in basic terms what LUN and RAID are, but how do they relate to each other?
If you have 20 disks comprising your total storage, what confuses me is that you can divide it into several different RAID groups, but that you can also divide it into several different LUNs as well.
So I don't see how both concepts relate to each other. Are they parallel, unrelated concepts, or is there something I'm missing here?
Thanks.
# 1
You might want to reference the SNIA dictionary. at http://www.snia.org/education/dictionary/ for some of these but you're basically running into slightly parallel concepts and some convoluted definitions as the technology has changed over time.
The short version is that different types of arrays allow you to export raw disk drives in various ways. The exported entry is known a lun. In some cases that lun is a single disk drive. In some cases its an entire single RAID group. In some cases you can take sections of that RAID group - Sometimes called a slice or a volume - and export that section of the RAID group has an independent lun. In some cases you can take RAID groups, combine them, and then take a slice that you export as a lun.
In many arrays the slice at the array level is called a volume. When you hear terms like "volume copy" or "volume migration" it implies that the operations are taking place behind the arrays ports.
