Accepted Solution

Disk shelf’s and cabling??

Would someone please be so kind as to explain a few things for me?

- I would like to know the main differences between the disk shelf models (ds4243, ds14mk2 & mk4)

- Also, how the shelf’s are cabled together assuming this is a single system with dual controllers

- Any documentation/diagrams to help me understand the best practice for cabling shelf’s

- When would SAS cables be used instead of fibre

Many thanks in advance

Re: Disk shelf’s and cabling??

DS14mk2 and DS14mk4, these are 2 generations of the same module. an ESH (Enhanced Switching Hub???) module that works at 2GB or 4GB (hence the names). You can have ESH2 modules in either shelf, but ESH4 modules would only work in a DS14mk4 shelf. These are both FC only, although that can be via a copper interconnect of a normal FC cable with GBICs. Your whole disk loop wants to (ideally) be the same speed so you'd get full 4GB or dedicated 2GB. Maximum of 6 shelves per loop, disk shelves need to be uniquely numbered in each loop.

DS4243 (DS = Disk Shelf, 4= 4U high, 24= number of disks, 3= 3GB SAS (although it has 4 in the SAS matrix making 12GB)) is a SAS only shelf, so these use SAS cables rather than FC.

The cabling is pretty much the same for either disk shelf. To create HA cabling (recommended) you'd connect one storage controller to the top disk shelf controller, then loop down each top shelf controller to eachother. At the bottom the connection goes back to the partner storage controller (opposite of where you started). The bottom storage controller would be the reverse of the first, so partner controller starts, back into the primary controller at the bottom. It doesn't really matter which order you do this in, so long as you have redundant paths across different loops to each system. Disk ownership is software based, so don't worry about cabling the owning controller into certain disks as you can soft change this when the system has booted.

The only additional cabling you'll want to be aware of is ACP (Alternative Control Path) which controls the active data path for SAS disk shelves and allows for advanced load balancing and failure detection in the loop. You really want this if you have more than 2 ACP shelves, but the cabling is a bit too complicated to explain in words. It's slightly different than the shelf storage cabling, you basically create one giant loop out of Ethernet cabling through all the ACP connections and shelf controllers then back to both storage controllers. You need a standard Ethernet port on the storage controllers, or the E0P port on the 2040.

Documentation -> Disk Shelves -> Disk Shelves (the anchor link is broken for the first link and it has a space in it!)

DS4243 Installation and Service Guide:

DS14mk1,2,4 Hardware Service Guide:

DS14mk2 AT Hardware Service Guide:

Re: Disk shelf’s and cabling??

Many thanks for this help!

I only have guest access (N Series Partner) so cant access DS4243 Installation and Service Guide - Can I get this document elsewhere?

Re: Disk shelf’s and cabling??

Hi Chris - I switched all modules to 4Gb and the Loop A Loop B lights are flashing.

I expect I have a DS14mk2 or two in the loop - how do I tell which are only 2Gb capable?


Re: Disk shelf’s and cabling??

We have put esh4 in mk2 shelves. Supported but only at 2gb. With 8.1 customers can't use esh2 so we are doing some swaps in existing mk2 shelves. To see if mk2 or mk4 check the speed switch. 4gb selector only on mk4 or environ shelf to see all shelf details.

Re: Disk shelf’s and cabling??

Ok, these are all MK4's with the switch set to 4

All lights are green on the back for the loops

But the Loop A and Loop B are flashing constantly and none of the disks are showing up

Any ideas how to diag this?


Re: Disk shelf’s and cabling??

You power cycled the shelves? Changes 2 to 4gb while powered off?

Re: Disk shelf’s and cabling??

I thought it was the shelves as well as the modules? if its just the ESH2 that’s somewhat cheaper than the prospect we have of having to throw away 26 shelves of 300gb FC disks ;S

Re: Disk shelf’s and cabling??

To go 4gb you must have esh4, mk4 and 15k 4gb drives. 10k and some older 15k are 2gb only drives.

Re: Disk shelf’s and cabling??

These are 10K RPM drives - thanks for the explanation!