I own a mainboard with sata raid support (sil 3112A). I plugged two identical sata devices in.
I can set Raid 0, and expect they would be shown as one device with nearly twice the capacity of each single disc. I boot arch setup, and see sda ... and sdb. I thought a stripe set would work as one virtual device? I wondered if each device, sda and sdb, are a stripe sets, each of them stored on half of the two discs (set0=half of sda, half of sdb, set1 = half of sda, half of sdb, but set0 is named sda, set1 is named sdb):
discs hosted stripe sets*
sda sda*, sdb*
sdb sda*, sdb*
alias set0 set1
Then sda, sdb would apparently be the nodes for the discs, and in reallity be the nodes for the stripe sets. Could this be true?
If I set Raid 5, I expected the discs would show up as one disc with the capacity of one single disk. Wonder what, again both sda and sdb appear.
Frumpus ♥ addict
as I understand it:
you need at least 3 drives for raid5 which results in a single lun (virtual disk). If you have n drives your capacity would be n minus 1 multiplied by the capacity of the lowest capacity drive in the array. You can lose one drive in the array and your good.
2 drives in a raid0 would be one lun (virtual drive) with a capacity equivalent to the sum of the capacity of both drives. If either drive fails start looking for your backup.
I read the linux user magazine, they had a sata raid test, and found out, sil3112a is kind of a dummy. It really does nothing.
Frumpus ♥ addict
a lot of the "hardware" raid solutions on motherboards are really little more than a small intrepreting bios that works well with windows. i've never been able to set it up in linux as a "hardware" solution, that is the card passes the array as a single drive to windows ie:
you create an array via your motherboard raid bios, you boot up windows and it sees a single drive of large size
in windows this is a cinch, in linux.. well.. good luck.
if you really want to do the raid 0, use the raid card as a controller card, just let the drives function as they normally would. then setup software raid using mdadm or raidtools. the sil 3112a is a hardware chip, but i dont believe it takes care of any operations itself, so you should see no preformance decrease using mdadm versus setting it up within the bios on your onboard controller.
as shbang said you do need 3 drives to do raid 5, but in the end its the best comprimise of speed, security, and storage. I run two raid 5 arrays myself and they've been running strong for 4 years.. who says ide drives dont last 8)