RAID Configuration, Continued
6. RAID Configuration, Continued
Step 4: After the MegaRAID software is finished scanning, your screen will look like Figure 13.
Figure 13: Array selection menu screen
You'll now select the drives for your array. In Figure 13, you can see three of the four hard drives attached to this computer. The first row, with "M" underneath each Channel column, shows "Master" hard drives. The second row is "S" for "slave" hard drives. Because the MegaRAID i4 is an IDE/ATA device, you can have up to 8 drives per card in a 4 master, 4 slave configuration. The missing hard drive in Figure 13 is Channel-3 (i.e., the fourth hard drive) which is not shown because an 80-column character-based screen is not wide enough to show four drives.
Now that we see all the drives that are going into our disk array, we need to tell the MegaRAID software which of these hard drives to use. Not all hard drives have to be used in the RAID 5 array. If you have four drives, you can put three drives into a RAID 5 array, and use the fourth drive as a hot-spinning spare for recovery.
To select all the drives for our array, we use the arrow keys in Figure 13 to move the cursor to a hard drive that says Ready, and then we hit the "Space" bar to toggle the drive's status from "Ready" to "Onlin" (yes, the "e" is missing!).
Figure 14 shows what the screen looks like after I've scrolled through each of the hard drives and hit "Space" to select each hard drive for the array. It actually is the same as Figure 13, except that the drives have changed from "Ready" to "Onlin".
Figure 14: Drives selected for the RAID array
To select the hard drive on Channel-3 (not shown off to the right of the screen) just use the right arrow to scroll to the right to find it, and then hit space bar.
As you can see, the MegaRAID user interface is clunky, but it's not too bad once you get the hang of the implicit rule of this interface: "when in doubt, look at the bottom row of the screen." The black magic around RAID 5 then disappears, and you can become comfortable with the MegaRAID.
Once you have all the disks showing a status of "Onlin"(as in Figure 14) look at the bottom row of the screen (see Figure 15).
Figure 15: Status line after drives are selected
Step 5: Then convert the selected drives into an array. Hit "Enter" to tell the MegaRAID software you are done selecting drives. After this, the screen will remain unchanged. Next, hit
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An excellent article. I have been trying to setup something like this. I just went thru 2 weeks of trying to get software raid 5 to work in Ubuntu. I searched the net for how-to or step by step instructions and could only find bits and pieces. Nothing worked. Linux users need to remember that us wanna bees don't know even the slightest of commands! In every article I found, they assumed you knew "some" basic commands. I tried reading and learning, but I couldn't find a good learner for linux. Anyway, having decided to do a hardware raid 5 with Ubuntu desktop seemed like my only hope. Then I find this article here, and it is exactly the way EVERY article should be done, step by step, assuming the reader knows nothing. This article is VERY good and thorough! Congratulations Benjamin Webb, you did a great job! -Blueuniform
interesting article, but the beauty of linux software RAID5 is that an array rebuild will happen automatically when you replace the faulty drive (well you have to tell it that you replaced the drive using mdadm). you can even simulate a failure and then watch it rebuild the array to get an idea of how your system will respond under different scenarios. here's a snippet of what needs to be done to replace the missing drive/partition:
Rebuilding:
To remove the failed partition and add the new parition:
mdadm /dev/mdX -r /dev/sdYZ -a /dev/sdYZ
where X is the array number (0,1,etc) and YZ is your disk/partition (sda3 for example)
e.g.:
mdadm /dev/md0 -r /dev/sde3 -a /dev/sdr3
(where sde3 is the 3rd partition on your faulty drive, and sdr3 is the 3rd partition on the new drive)
Watch the automatic reconstruction run with:
watch -n1 cat /proc/mdstat
I understand that people fear the console commands. It can be a bit scary at first. But mdadm is pretty simple when you're used to console apps and a little bit of linux. It's mostly just mdadm and such. I currently run two software raids with 7 and 5 disks.
i believe his concerns with software raid5 were not just the rebuilding points. i believe he liked the fact that if the os drive took a crap, he could take the card and array and move it to any operating computer and it would power up and work. if you lose the operating system that wrote the software raid array, you have lost the array.