RAID on a home desktop PC ...

[jamesbandido]

RAID system on a home desktop PC ... is this possible ? if so, what would i need or the minimum specs that my desktop PC should have ?

thanks in advance.

[E1PHOTON]

You'd need a RAID controller if you want to do a hardware based RAID setup, or you can get some software based RAID programs that do a pretty good job, too.

James

[Satanic Atheist]

I use mdadm to do all my RAID stuff and it's pretty good. I can use RAID on an external hard drive setup or internal drives.

Note: Windows can't do this - it refuses to do RAID on anything but Windows Server edition and even if you fiddle it to think it's Windows Server, you cannot do RAID on anything but SATA/PATA drives and definitely not on a laptop (completely disabled).

Now, the basic way of setting up a RAID-1 mirror system is this:

Have two drives, at least one of which is blank.

Create the array on the blank drive (or both drives if they're both blank). This generates /dev/mdx device node that you can use. If both drives are blank, simply create the filesystem on the md device node and off you go. If, on the other hand, only one of the drives is blank, you need to copy EVERYTHING across to the /dev/md device (essentially now the spare drive) and (if it's bootable) setup GRUB on it. Change GRUB so that you can boot of either drive and reboot onto the RAID drive (which is currently degraded). Once you're there, flatten the original drive and recreate the partition table exactly as it is on the RAID drive and add it to the array. The array will then automatically rebuild itself which can take a while depending on size of drive etc.

Then, all going well, check /proc/mdstat and it will show you the RAID array similar to the following:

Personalities : [raid1]
md1 : active raid1 sda2[0] sdb2[1]
3895680 blocks [2/2] [UU]

md0 : active raid1 sda1[0] sdb1[1]
240235904 blocks [2/2] [UU]

unused devices: <none>
Hope this helps. If you need specific help on each stage then post back and I'll dig out my notes for you.

James

[trilarian]

/second mdadm. I'd say unless you are planning to buy multiple top-end drives, the hardware controller is not worth the money. mdadm on small arrays can perform very well and does not require a lot of overhead.

I went with the stripe RAID-0 for speed (only advised if you do regular backups to another source). I have a DVD-DL burner that I make regular backups to, so I didn't need the mirror. I also tend to fill drives up quickly (4 TB worth of crap on DVD and another 2 TB worth on the server), so I couldn't justify the wasted space in duplication.

I also partitioned the RAID array using LVM which helps with me changing up my partitions. My fstab looks like this:

# <file system> <mount point> <type> <options> <dump> <pass>
proc /proc proc defaults 0 0
/dev/mapper/raid-root / ext3 noatime,errors=remount-ro 0 1
/dev/md0 /boot reiserfs notail 0 2
/dev/mapper/raid-var /var ext3 defaults 0 2
/dev/mapper/raid-swap none swap sw 0 0
/dev/mapper/raid-documents /home/trilarian/Documents xfs noatime 0 0
/dev/mapper/raid-music /home/trilarian/Music xfs noatime 0 0

[Satanic Atheist]

Just out of interest, is it possible to boot off of a RAID-5 array using mdadm? Anyone managed this? I don't think it's possible and you would need a boot partition to get the machine started but if it is, then I'll be fitting another hard drive to my array later on!

James

[trilarian]

From the docs (http://www.gagme.com/greg/linux/raid-lvm.php):

There is one limitation with Linux Software RAID that a /boot partition can only reside on a RAID-1 array.

/boot doesn't have to be large though. In my setup, everything is RAID-0 except the /boot which is RAID-1. So I lose 50MB to duplication of my /boot, but 50MB is nothing when compared to the 2TB capacity.

[Satanic Atheist]

I suspected as much. Shame really, but it's not really possible to rely on the boot stuff being on the first disk simply because of the nature of RAID. Oh well, I'll just have to live with 250Gb capacity of RAID-1 storage!

James