Assembly
4. Assembly
You need a case that will allow four hard drives with a full hard drive's worth of space between them. Figure 4 shows the #1 feature I look for in a case: a drive tower that runs from the floor of the case all the way up to the underside of the externally mountable devices (i.e., the floppy and optical drives). I have found that trying to squeeze hard drives into a case that does not have extra space is a sure way to cook them.
Figure 4: Case detail
Next, lay out the RAID 5 components. To make the NAS you need to basically start with a standard desktop computer without a hard drive. In Figure 5 I've already installed the motherboard, RAM, CPU, optical drive and power supply, to make a standard desktop computer that is ready to go except for the hard drives.
Figure 5: Ready for assembly
Then, install the hard drives one at a time and hold them in place with one screw. I leave a full drive's worth of space vertically between drives in the case, for better cooling.
Install the power cables to each drive, then install the ribbon cables on the MegaRAID i4 card and insert the card into the PCI slot. Figure 6 shows the four drives installed and powered, and the MegaRAID card with 4 IDE/ATA ribbon cables hanging off, ready to be attached to the 4 drives.
Figure 6: Drives installed waiting for RAID cable connection
TIP: I advise installing the cables before you put the MegaRAID card into the computer. The connectors on the MegaRAID card can crack if you wiggle the ribbon cable towards and away from the face of the card. Installing the cables while the card is outside of the case greatly lowers this risk.
After the MegaRAID i4 card and cables are installed, connect the ribbon cables from the MegaRAID i4 to the hard drives (see Figure 7).
Figure 7: Drives cabled up
At this point you can add the second screw to each hard drive and button up the case. I've never set a jumper on a hard drive when using a MegaRAID card. I simply take the hard drives out of the box, put them into the computer case and don't even look at how the jumpers are set.
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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.