Re: how to fill 5887's

[DrFranken <midrange@xxxxxxxxxxxx>]

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

www.frankeni.com
www.iDevCloud.com
www.iInTheCloud.com

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