Dell PowerEdge SC1435 and PowerVault MD1000

This is about getting the Dell PowerEdge SC1435 working with the Dell PowerVault MD1000. I bought two PEs and a PV for each of our sites, one in China, one in the US. Evidently, I should have done more research before choosing this combination, because it’s known not to work. However, our Dell salesmen (both in China and the US) still happily sold it to us. At this point, the system now does what we need, but only after quite a bit of hassle. Maybe this will save the next person some headache if they find themselves with this combination of hardware in their hands.

There are two main aspects to this problem, one hardware, and one software.

Hardware incompatibility

The SC1435 can’t be ordered without at least one internal disk. We ordered ours with two SATA drives and asked the Dell salesman not to put the “SAS 5IR SAS, PCI-Express Internal RAID Adapter (341-3756)” in the machine since we didn’t need it. The Dell salesman wrote back,

The SAS controller card in the SC1435 does not add any cost. Since
hardware RAID is faster than software RAID it seemed better to leave
that item in the server.

The servers and array arrived, and the first thing I found was that the SAS 5IR occupies the SC1435’s single PCI slot. To control the MD1000, I had ordered a “PERC6E SAS RAID Controller 2×4 Connectors, External, PCIe512MB Cache, Customer Install (341-5899)”. This installed nicely in place of the SAS 5IR.

The trouble is that the connector for the drives on the 5IR is not the usual L-shaped SATA connector; it is a single connector of a type I’m not familiar with, and can not be reused to attach the internal drives to the motherboard’s integrated SATA controller.

We talked to the Dell salesmen about this, and they both said that attaching the internal drives to the onboard controller is not something their contacts in Dell Support had heard of doing. They also both claimed that because of the newness of this platform, we were running into this situation for the first time. The Dell salesmen asked us to confirm, using SATA cables borrowed from our desktops, that our suggested configuration would work, whereupon they would get us the correct cables.

Using ordinary SATA cables works fine, except that using a straight connector on the motherboard causes the cable to jut upwardly high enough that the lid can not be closed.

The Dell salesmen told us that Dell Support would find us the correct cables for the machines. In the US, they sent us some pretty blue 7″ Dell-labeled cables with an angle on one end. Only one cable would work, though, because the second drive was just out of reach of the cable. (They charged us $4 each for these cables.) They then sent us two different cables, this time some generic red cables with angles on both ends (from their appearance, these might’ve come from Fry’s, or perhaps out of the Dell dumpsters). These couldn’t be installed, because the angle on the drive side angled down into the floor of the chassis. (They charged us $9 each for these cables.) After several emails back and forth over many days, they finally sent us a pair of pretty, blue 19″ Dell-labeled cables that were way too long but did the trick. (They billed us yet again for $9 each, but this time our CEO yelled at the Dell salesman for repeatedly charging us for the wrong cables, and they refunded us.) Whew!

In China, we haven’t been so lucky. Our formerly enthusiastic Dell saleswoman is now ignoring our communications after several weeks of back and forth, though the last we heard from her, she’d located some 10″ cables with one straight and one angled connector that would have done the trick (if they’d only ever been shipped). When I can, I’ll put the part number here to save the next person some trouble.

Update:Dell China finally sent us some cables, part number HK010, description “ASSY,CBL,SATA,LG,SC1435″. These cables are the perfect length, and the connector is angled the correct direction on one end to connect to the motherboard, and is straight on the other end to connect to the disk. Unfortunately, as our luck seems to be going, they sent us only 3 cables, so we can only cable up 1.5 of our 2 machines.

At this point, we are still running with the boxes open (the mobo detects this and turns up the fans to compensate; boy, do they scream!). However, we have both internal and external disks attached properly. Once we get the correct cables, we’ll be able to close up the machines and deploy them to the IDC.

Software incompatibility

According to a recent linux-poweredge mailing list post, OpenManage Server Administrator (OMSA) won’t run on the SC series because the SC series is the cheaper line of machines and doesn’t have all the features of other lines. Unfortunately, OMSA is needed to administer the RAID array from within the OS. The good news is you can still install OMSA with a little trick.

The trouble is that the install of the srvadmin-syscheck RPM will fail with “srvadmin-syscheck: This RPM is not supported on this system”. This check will be ignored if the environment variable “OMIIGNORESYSID” is set to a non-zero value (check the RPM’s %pre script for more information). In a kickstart install, this variable can be set in a %pre script in the ks.cfg.

Testing results and conclusions

Despite the difficulties getting the machines up and running and despite that we’ve been sold a configuration that is unsupported by Dell (I fear that when we experience a hardware failure, we will have to go through all this headache once more), the machines are now running quite happily, and otherwise perform as expected. We haven’t had any stability problems in our tests, and we’ve been able to get all the required functionality from the hosts.

I was talking with the top architect of a large university’s campus IT organization, and he nailed the problem when he said we are “trying to have it both ways–commercial support with commodity hardware”. This doesn’t explain why Dell is willing to sell these products together, but it describes well our goal. However, we ended up with the opposite: the system cost more than one built from commodity hardware, but we now have to support it ourselves.

As an aside, even with the fancy PERC6/E, it appears that software RAID is as fast as hardware RAID for a 6-disk array, and actually way faster for block reads, according to Bonnie. Don’t automatically believe your Dell salesman about this!

              -------Sequential Output-------- ---Sequential Input-- --Random--
              -Per Char- --Block--- -Rewrite-- -Per Char- --Block--- --Seeks---
Machine    GB M/sec %CPU M/sec %CPU M/sec %CPU M/sec %CPU M/sec %CPU  /sec %CPU
H/W R5      5  42.3 97.9 172.1 46.9  57.9  6.4  41.9 64.2 161.5  3.4   255  0.1
S/W R5      5  43.1 98.5 179.0 48.9  60.5  8.9  48.9 89.6 278.2 21.5   272  0.0