SSD placement in 3PAR 7400 system

[SatishJ]

Hello,

We have procured a new 3PAR 7400 system with 12 SSDs, 6 hard disk shelves and 144 hard disks. There are plans to add 12 more SSDs sometime in future.

What is the ideal place to locate the SSDs ? I felt that they should go in the head unit as (hopefully) the communication inside the head unit would happen on some sort of high speed bus. If the SSDs are placed in one of the shelves, the communication would happen on the backend SAS path. I was wondering if this would present a bottleneck under some circumstances.

The HP installation engineer has told us that the best practice is to spread the SSDs across all disk shelves. I wonder how this helps and not really convinced. Does anyone have inputs and/or practical experience in this area ?

Any help would be much appreciated.

Regards

[Dennis Handly]

I've never head of a "head unit", all drives go into cages.

(But each node has a disk for its OS.)

>best practice is to spread the SSDs across all disk shelves

Sounds right to me if you want HA.

[SatishJ]

Hello,

By 'head-unit' I meant the unit that has the FC or iSCSI controllers inside it. Rest of the drive enclosures connect to this unit through SAS. Please have a look at the attached image.

Regards

[SatishJ]

The part number for the disk enclosure is M6710. Please check the attached image. This box has SAS connectivity and nothing else.

[3Par_Eng]

The drives in the controller enclosure/cage also uses the same SAS backend as rest of the cages. So there is no advantage of putting all your SSD drives in the controller enclosure.

Assuming this is a 2 node array, you should spread your SSD drives evenly accross all the cages (i.e. 2 per cage)to get the best usable capacity, performance and availability.

[Dennis Handly]

>By 'head-unit' I meant the unit that has the FC or iSCSI controllers inside it.

This is a node.  There is little room for disks in there and I'm not sure you could connect it to both nodes?

And most important of all, the software only expects the disks to be in cages.

[Sheldon Smith]

The IO paths to the cages on the front of the controller pair are no different from the IO paths on the M6710 drive enclosures. Spread the SSDs in pairs, evenly, across all the cages including the cage of the 'head unit'.

Note: While I work for HP, all of my comments (whether noted or not), are my own and are not any official representation of the company.
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