I am about to replace an ESXi host that runs some 20 VMs (mostly idling). Today around only 800Gb is used on an external iscsi-box, raid6 (total 7Tb).
The new server will just simply have internal disks. 2Tb will be plenty. It will most likely be a Dell R640 (max 8 discs). ESXi will be on a simple raid1 (2 small discs).
But the VM-storage? Which should i go for? (the HDDs are slightly cheaper, but no big diff).
A. 3 SSDs (960Gb) Raid5 = 2Tb
B. 6 HDDs (600Gb 10K) Raid10 = almost 2Tb
The server will have a dedicated raid-controller (perc) of course.
RAID5 with SSD gives you much better performance on random I/O, approx. same redundancy level and scale-up slots. The suggested in comments configuration with cache makes no sense in my opinion, because it will cost more (or same) than SSD only storage, but it adds unnecessary complexity for storage and has lower performance.
You may find, that RAID5 is not recommended RAID level. It relates more to HDD drive, especially large capacity, because of two main reasons: slow random write performance; long and “potential risky” rebuild. SSDs works good in RAID5. Here more detailed description - https://www.starwindsoftware.com/blog/raid-5-was-great-until-high-capacity-hdds-came-into-play-but-ssds-restored-its-former-glory-2