If I understand the way SAS works there is essentially a group of connections, paths, on each cable. Typically four paths of 6Gb each in current technology. There is an additional port 'on the other side' of the controller with four more paths connected to the other RAID card. This is a completely separate connection to the disk units. Each disk in fact has two independent paths to it.

The data comes down those cables with an 'address' on it indicating which drive the data or command is for. There is an expander in the drawer that directs the data to the correct physical drive through the backplane.

SO I don't believe there is any difference in slot 1 or slot 9 or slot 24 for that matter. The four paths on the cable are all used and the expander on the back-plane in the drawer will deliver to any drive at any time at the same speed as I understand it.

Careful though, if you put spinny drives in there you'll bollix up the works because the paths to that drawer are now potentially tied up waiting for those slower disks and the SSDs get queueueueued. (I know you didn't suggest that you would but just a warning.)

- Larry "DrFranken" Bolhuis


On 6/27/2014 3:23 PM, rob@xxxxxxxxx wrote:

New Power 8. CEC disk is for VIOS only (at least in our config). Have
two 5887's. Each has three 8 drive bays for a subtotal of 24 for each
5887 or 48 drives I could load total for both 5887's. I am loading 34
drives. All SSD's. I will have more space than I'll need for the
foreseeable future. Lots.

Question 1: Should I balance them among bays? For example, use slots
1-6, 9-14, 17-21 for 6,6,5 of each 5887? Or should I just start from the
left and go right, and just balance them between the two 5887's?

Question 2: Going to use RAID5 with hot spare. Should I select create
raid sets for performance (or however that's worded)?

Rob Berendt

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