Raid 5

[Philippine Mango]

Is it possible to have a raid 5 configuration with more drives? It seems like saying a "raid number" is the method of data disposal and retreival but you can have an infident amount of drives, is this true?

 

[KK]

I'm not sure as to what exactly you are trying to get answered. The number of drives you can have on you raid 5 system depends on the controller card you are using. I'm using a promise 6000 card that allows up to 6 drives, I only got 5 attached though. The most I've seen a controller card being able to handle was 12 SATA drives. I'm not sure if there is any commercial type controllers that would give you more drive capabilities or not.

 

[deveraux]

Yes, RAID 5 is for an unlimited number of drives. However, the more drives you attach, the slower it will usually be dual to the parity bit calculation. But, your read speed should be very much higher.

EDIT: And if you want to do RAID 5, you MUST make sure that the controller has an ONBOARD chip to do the parity calculation as well as the rest of the RAID 5 calculation (no software) or it WILL bog your CPU down a lot.

 

[Daynja]

RAID 5 requires 3 drives minimum, but in theory there is no maximum. I know there are controllers out there that support 16 drives (using 2 cards), and I'm sure there's some that support even more.

btw, my software raid 5 doesn't bog down the system (2.8GHz) , but the max sequential read speed is right around a single disk at 40MB/sec. I dunno what the problem is. While doing tests the processor usage averages less than 10%

 

[Vegito]

one scsi chain usually supports 15 -1 (controller)

some scsi card has dual channel supports 29 drive, 1 for controller..

I have 14 drive arrays on dual channel since having all 14 drive on 1 channel will decrease your total available bandwidth (u320s)

7 drive sharing a u320 bandwidth is less crowded than 14 drive

 

[Philippine Mango]

On the PCI-X bus (64bit) is each peripheral connection independent or is it just like the PCI bus, seems like despite adding more controllers you still have the bandwidth limitation of how much PCI or PCI-X has (133MB/S for PCI) I dunno for PCI-X. Raid 0 has no drive limitation as well, correct?

Originally posted by: deveraux
Yes, RAID 5 is for an unlimited number of drives. However, the more drives you attach, the slower it will usually be dual to the parity bit calculation. But, your read speed should be very much higher.

What do you mean it will be slower due to parity bit calculation if the read speed will be faster? Wouldn't it coinside and it would be some sort of ratio? Anand did a test with software raid and was able to get 75MB/S, what exactally is limiting it to ONLY 75MB/S?