Question to the Storage Advisors: Craig: We are working out the design of a new storage server. We need space over speed in every possible way. This server is in effect near line storage. We want to use RAID 6 or 60. My question is how many disks is it recommended to have in a single RAID 6 set. We will be using 2TB SATA disks. In the past we have used 14 disks in a single RAID 6 volume and had ok results with this. Also is there any rule of thumb for hot spares?
Craig … don’t be too keen to get too close to the bleeding edge here. While you may want to squeeze all possible space from your server keep in mind that when things get bigger they take longer.
So … when building a single RAID 6 you can have up to 32 drives. When building RAID 60′s then 16 drives per leg with as many legs of a RAID 60 as you want.
I think 32 drives in a single-level RAID array is nuts. I’ve told engineering that one before but no-one listed to us dumb Aussies so it falls on deaf ears. Since you don’t seem to care about performance and haven’t specified how many drives you are going to use for this thing, a rough rule of thumb would be that up to 16 drives use RAID 6 … over that move to RAID 60.
As for the number of hot spares to have for any given RAID array? I’ve never seen a mathematical equation that formularises this, and have always found that quantity of hot spares normally is a result of working out how many spare slots you end up with in your server after making your RAID arrays. So a general rule of thumb would be 16 drives or less have one hot spare … anything over that have at least 2 spares. 3 would probably be considered max.