VMware vSAN on Cisco UCS Part 1 – Hardware

I have had parts of this post saved in draft for months without getting it finished because it was turning to a monster of a post if I tried covering it all. I finally found the drive to finish it when I realized that this was probably better if I split it in multiple posts instead of trying to include hardware considerations, UCS manager / standalone profile configurations and ESXi configurations into one single post.

So without further ado lets dive into the hardware part of VMware vSAN on Cisco UCS.

Please do note that these are my personal opinions and may or may not align with what you need in your datacenter solution. Most designs are individual for at specific use case and as such cannot be taken directly from here.

Base models

Cisco has a bunch of certified vSAN Ready nodes based on M4, M5 and M6 branches of servers. M3 isn’t supported as the hardware is both EOL and most of the controllers available for M3 models weren’t powerful enough for running vSAN workloads. The most common to use are Cisco’s C240 M5SX 2U models which allow for 24-26 drive bays total. For smaller deployments the C220 M5SX is also an excellent option with up 10 drives in 1U.

It is technically possible to run vSAN on other types of servers like the S3260 and B200 blades but they limit your options in terms of storage to compute ratio (S3260 being able to provide massive amounts of storage but little in compute and B200 being the opposite due to only having 2 disk slots).

One thing to note is if you plan on using NVMe storage options you need to focus on M5 and M6. M5 allows for up to 4 NVMe devices in U.2 format while M6 can support up to 24 NVMe devices. M4 only supports PCIe NVMe devices.

Boot options

Cisco has traditionally been a network boot company and as such the primary local boot option on M3 and M4 is SD cards if you don’t want to waste disk slots on boot devices. On B200 M4 with only 2 disk slots SD card is currently the only option as the disk slots are needed for a caching and capacity disk. On all M5 and M6 models (B200 included) there is a new dedicated slot for inserting a UCS-M2-HWRAID controller which can fit 2 M.2 drives (either 240 or 960 GB) and can do actual RAID that ESXi supports. Do not use the UCS-MSTOR-M2 controller which fits the same slot and fits 2 M.2 as well but this only supports the onboard LSI-SW RAID from the Intel chipset and that is only supported by Windows and Linux and not ESXi. It is not that expensive – just by the HWRAID controller 🙂

Specifically on the C240 M4 if you choose a UCSC-PCI-1C-240M4 you can insert up to two drives internally in the server that are managed by the onboard controller. You won’t have RAID functionality but it beats SD card booting by miles!

NIC

My go to here is using M5 servers with a UCSC-MLOM-C40Q-03 (VIC 1387) in combination with 6300 series Fabric Interconnects. That provides 2x40G per server which pairs nicely if your upstream network is 40 or 100G. On M6 that would be UCSC-M-V100-04 (VIC 1477) that provides the same.

If you are using 6400 series Fabric Interconnects and a 25G infrastructure you might want to go with UCSC-MLOM-C25Q-04 (VIC 1457) on M5 and UCSC-M-V25-04 (VIC 1467) on M6 to give 4×10/25G connections instead. Depends on your infrastructure.

On M4 it is technically possible to use the UCSC-MLOM-C40Q-03 (VIC 1387) all though the UCSC-MLOM-CSC-02 (VIC 1227) adapter is way more common but only provides 2x10G connections. If you run a pure 10G infrastructure and continue to do so I recommend adding an additional UCSC-PCIE-CSC-02 (VIC 1225) to provide 2x10G. I see this combination primarily used with 6200 series Fabric Interconnects.

For blades the standard is UCSB-MLOM-40G-03 (VIC 1340) for M4 and UCSB-MLOM-40G-04 (VIC 1440) for M5 and M6. Both cards are 2x40G. These need to be paired with IOM’s in the blade chassis which can limit the speed of the vNICs presented. Usually you get 2x20G on IOM 2304 and 2208. Consult your Cisco vendor to confirm how to get optimum speeds for your setup.

Controllers

Now the probably most crucial part of the any vSAN deployment – the controller. Albiet less important if you go for all-NVMe or even the new ESA option in vSAN 8 you need at SAS/SATA controller to handle your disks.

On C240 M4 this is usually UCSC-SAS12GHBA or UCSC-MRAID12G with a UCSC-MRAID12G-1GB cache module. Both are on the HCL but SAS HBA is prefferable over the RAID controller

On C220 and C240 M5 the only real options for vSAN are UCSC-SAS-M5 and UCSC-SAS-M5HD respectively. Primary difference is how many drives the controller is capable of utilizing which of course needs to be higher for the C240.

On the C240 M6 the option is CSC-SAS-M6T (UCSC-SAS-240M6) which allows for up to 16 disks but to be honest – if you are going for M6 nodes you should probably go for an M6N og M6SN for all NVMe configuration instead.

Disks

I won’t touch too much on this as various use cases and requirements need different numbers of disk groups and capacity devices. You use case may vary. We primarily use 3.8 TB Enterprise Value SATA SSD’s for capacity simply because they are fast enough and readily available to us. We aim to use NVMe caching devices if at all possible but if not we select a high endurance and performance SAS SSD for caching.

One note to have in mind. M4 only supports PCIe NVMe devices. On the C220 M5SX two front slots can be used for NVMe and on C220 M5SN all 10 slots can be NVMe. On the C240 M5SX slots 1 and 2 as well as 25 and 26 (on the rear) can be used for NVMe’s and on the C240M5SN bays 1-8 can be used for NVMe.

If you are retrofitting NVMe’s into existing C2x0 M5’s note that on the C220 M5 you need a CBL-NVME-220F to be able to use the front facing NVMe drives if not already present.

On the C240 M5 I recommend going for a UCSC-RIS-2C-240M5 which supports both 2xfront and 2xrear mounted NVMe’s if you remember to order a CBL-NVME-240SFF and UCSC-RNVME-240M5 to connect the front and rear slots respectively to the riser. This configuration allows you up to 4 NVMe caching devices while using SAS/SATA capacity drives up to 5 drives per group which can be a lot of disk and performance.

Conclusion

So those are the notes on hardware I have. I have not touched on CPU types and memory configurations at all as this is something that needs to match your workload. Somethings might need 3.0 Ghz base clock and no memory or loads of cores and memory. Pick something that matches the workload but I would recommend sticking to Xeon Gold CPU’s to get a good balance of performance and cores and selecting a configuration of 12 DIMMs for M5’s to get maximum memory bandwidth.

In the next article I’ll touch on the UCS Manager configurations that I use for vSAN.