2

Reading the D2600/D2700 User guide, there's a section called "Cabling examples", but none of the examples match what we intend to do.

I just want to make sure that it makes sense, before we do it.

So here's the plan:

We have 1xP822 in a Gen8 rack server and 2xD2700 enclosures. We have 24 drives in each D2700. Both D2700 is configured with the exact same disk layout. We create one RAID10 array on top of the D2700 enclosures (meaning one side of the mirror is on each D2700 enclosure - the HP ACU/SSM automatically makes sure of this).

We then connect the P822 controller with 4 cables in total to the D2700 enclosures (NO cascading):

P822 Port 1E: D2700 box1, IO Module A P822 Port 2E: D2700 box2, IO Module A P822 Port 3E: D2700 box1, IO Module B P822 Port 4E: D2700 box2, IO Module B

Not thinking about the expansion options here, would this be the correct way of cabling, in terms of getting maximum performance from the drives/enclosures/p822 controller?

Thanks :)

EDIT: So what I'm reading from the comments so far, is that this approach is not "WRONG/INCORRECT", it's just not really beneficial in any way?...

ewwhite
  • 201,205
N-3
  • 118

2 Answers2

1

I have lots of full D2700 enclosures... You will be oversubscribed at the enclosure level, due to the SAS expander backplane in the D2700. You'll have either 4 or 8 lanes of 6Gbps bandwidth available to you.

24 x 6Gbps-linked SAS disks, each really capable of 2Gbps == 48Gbps sequential capability (minus overhead).

That's versus your 4 x 6Gbps = 24Gbps SAS SFF-8088 link to the host.

You should be looking into a Dual-Domain configuration, where you're leveraging the multipath SAS connections between the host and the array and disks. This also provides some resiliency.

IOPS will be a function of workload and array layout, not the cabling arrangement.

Max throughput will be well below the PCIe 3.0 full-duplex 8 Gigabytes/second capability of the PCIe slot. The bottlenecks in raw throughput will be your D2700 enclosure, followed by the RAID controller.

There's no cabling arrangement that will yield an appreciable difference in that throughput, short of going to a dual-domain multipath configuration.

Community
  • 1
ewwhite
  • 201,205
-1

Depends on how you set it up and what exactly you mean by "performance"...

When connecting disk enclosures, the all around "best" option is to create a loop. In your situation that can either be 1 link "to" each enclosure and 1 link "from" each (note: SAS 2.0+ is bi-directional and routed, the "to" and "from" terminology is leftovers from SAS 1.0). Or you could do a pair of links to the first enclosure, cascade two to the second, and loop from the second back to the HBA card.

The latter topology (2 links HBA->EncA->EncB->HBA) would allow all 16 channels to be used by one enclose, or split between the enclosures. The former topology (2 links HBA->EncA & HBA->EncB) allows just 8 channels to each enclosure. If your load is split pretty evenly then either topology works equally well, and both are redundant.

Another thing to consider, the RAID functionality of the P822 is limited to 8 channels at a time. If you're intending to do a bunch of large hardware RAID configurations your bandwidth may be limited by this card. This is unlikely to be an issue unless you're pushing a lot of data all at once.

Chris S
  • 78,455