Mixing HDD with vSAN

[msidnam]

Hello everyone. I think the answer is yes but I wanted to double check since some of the other posts I have seen are a few years old. We are in the process of getting 3 more servers to add to our cluster. I tried to get the 3 new ones as close as possible to the ones we currently have but the older ones are about 3-5 years old. The new ones have a similar chipset and speed but the new ones have 16 core for each proc instead of 14 core for each proc. Also, the HDD are 10K 2.4TB while the older ones are 7.2K 2TB.

We will be replacing all the older ones with the same type of newer ones next year but I needed to get 3 more immediately. Do you think this will pose an issue?

Thank you.

[TheBobkin · Accepted solution]

@msidnam, this should be fine as you are adding/replacing components that are likely better performance than the other capacity disks and not massively different in size.

That being said, you would want to also be retaining or improving the Disk-Group rati/layout e.g. don't go from 3x capacity-tier in a DG to 6x capacity-tier in a DG and same cache size/performance.

[msidnam]

@TheBobkin Perfect, thank you. For the new servers I did get 2 1.92TB SSD for cache on each server. The current servers have 2 each as well (1.92TB). Is this ok to do or should I have gotten bigger SSD's for cache?

Thank you again.

[TheBobkin]

@msidnam No, actually smaller, faster (e.g. write-intensive) SSDs can be preferable over larger ones - in vSAN 7.x and earlier, only 600GB of cache-tier device will be actively used (1.6TB in vSAN 8.x OSA) and any size greater than this just used to prolong the lifespan of the device.

If they are similar (or better) performance spec SSDs to the current ones then this should be fine.