Is there an equation of something to figure out how many drives you can have on raid 5 or 6

[eflat]

From what I have been reading, almost everyone uses 4 drives with raid 5.

Can you add more? And is there a way to figure out the most efficient way to do so?

 

[MustISO]

I've done raid 5 with more than 4 drives. I'm not sure what's the most efficient, if I need RAID5 I use whatever drives we have and keep a few spares.

 

[MustISO]

I've done raid 5 with more than 4 drives. I'm not sure what's the most efficient, if I need RAID5 I use whatever drives we have and keep a few spares.

 

[Fullmetal Chocobo]

Yes you can add more; you can add as many as your controller can handle. I don't know about other controllers, but I know with Areca you can span controllers, so if you have 2 12-port controllers, you could have a 24-disk RAID 5 array. I'm not quite sure what you mean by finding the efficiency--efficiency of what exactly?

If you are referring to efficiency of hard drive space used for parity vs. available for storage, then there is a sort of equation you can use.

RAID 5
size_of_drive * (N-1), where N is the number of drives

RAID 6
size_of_drive * (N-2), where N is the number of drives

For both, the efficiency goes up with the more drives you use. In the case of RAID 5, if you are using the minimum number of drives (3), then 1 drive is essentially used for parity*. So you have 2/3 for storage. If you are using 10 drives in a RAID 5 array, the space of one drive is still used for parity, so you have 9/10 available for storage. The same goes for RAID 6, except the minimum is 4 drives, and the space of 2 drives is used for parity.

*RAID 5 rotates the parity bit on all drives, so no one drive is used exclusively for parity (that is RAID 3), but for the purpose of example, it works for how much storage is available, etc.

Hope that helps.