It seems Virtual SAN is on fire… I’ve been getting emails about VSAN configurations on a daily basis from partners, VMware field and customers. More and more customers seem to be looking at deploying Virtual SAN with a high number of disks and this week I ran in to something that I wanted to share with you. I thought it was common knowledge, but I guess I was wrong. If you are planning to have more than 8 disks / devices in your Virtual SAN host then it is good to know that you will either need a second disk controller (Check the HCL!) or use a SAS Expander! This design / sizing principle is listed in the VSAN Ready Node PDF, and should also make its way to the Design / Sizing Guide soon. The following is mentioned in the VSAN Ready Node PDF:
No more than 8 disks (SSD + HDD) supported behind a single controller. In case you need to add more than 8 disks, please add an additional controller.
I met up with the product manager for the compatibility guide and asked him which SAS Expanders are supported, he mentioned that support is done per platform and that the following vendors and platforms have just been update. Note that the HCL will still need to be updated for these:
- Dell SAS Expanders 5.5 and 6.0 hybrid. Supported on a specific configuration: H730 on 730d platform with 24 drives.
- Lenovo SAS Expanders 5.5. Supported on a specific configuration: Lenovo 720ix, RD650 platform with 12 drives.
We also are working on support for HP and Cisco (and others over time), and you can also expect an update on those soon. For now, keep in mind that when designing / planning for Virtual SAN the number of virtual disks may mean you need to change the configuration of your host.
This week I had the pleasure of talking to fellow dutchy
The conversation of course didn’t end there, lets get in to some more details. We discussed the use case first. PeaSoup is a hosting / cloud provider. Today they have two clusters running based on Virtual SAN. They have a management cluster which hosts all components needed for a vCloud Director environment and then they have a resource cluster. The great thing for PeaSoup was that they could start out with a relatively low investment in hardware and scale fast when new customers on-board or when existing customers require new hardware.
Harold pointed out that the only down side of this particular Fujitsu configuration was the fact that it only came with a disk controller that is limited to “RAID O” only, no passthrough. I asked him if they experienced any issues around that and he mentioned that they had 1 disk failure so far and that is resulted in having to reboot the server in order to recreate a RAID-0 set for that new disk. Not too big of a deal for PeaSoup, but of course if possible he would prefer to prevent this reboot from being needed. The disk controller by the way is based on the LSI 2208 chipset and it is one of things PeaSoup was very thorough about, making sure it was supported and that it had a high queue depth. The “HCL” came up multiple times during the conversation and Harold felt that although doing a lot of research up front and creating a scalable and repeatable architecture takes time, it also results in a very reliable environment with predictable performance. For a cloud provider reliability and user experience is literally your bread and butter, they couldn’t afford to “guess”. That was also one of the reasons they selected a VSAN Ready Node configuration as a foundation and tweaked where their environment and anticipated workload would require it.