This post is a quick run through on expanding a logical device using Adaptec Storage Manager (ASM). This feature is great for expanding the capacity of your RAID as is an online resize. This means that you do not lose access to your data during the process. On the other hand, it is not powerful enough to expand the array to fewer number of disks.
I learned this the hard way – I recently purchased a 128GB Agility 4 SATA III SSD to replace my 60GB Agility 3 (which was at this time the other part of the RAID stripe with a 120GB drive). For fun, I thought I would marginally increase the size of the array by adding the new drive and manually change the array size, keeping it under the limit of n*3 or n1*2 (where n is the size of the smallest drive, 60GB, and n1 is the size of the smallest drive in the conceptualized array, after I play with the configuration for a while, 120GB).
Once I ran the wizard (outlined below), and benchmarked the whole thing, which wasn’t all that impressive. I decided to increase the array size to the full 240GB using only the 2 larger drives and use the 60GB for something else.
Here’s where it all went downhill. Nope, you cannot decrease the number of physical devices in a logical array even if the total space is greater than the existing logical device size! I guess it would be a very complex algorithm or something. Now, I will have to create a system image and destroy the array, recreate it with the two drives and recover the system image to the newly created array. But first, lets add a 4th SSD!
Follow along with the images to see the process of expanding a logical device in ASM: