My system is PC based and I have a 6TB internal HDD which holds my original images (260k images) this drive is almost full this is backed up to an 8TB External HDD and to a synology NAS.
My catalogue is stored in dropbox on an internal M2 SSD the Catalogue occupies 4.04gb of disk space , smart previews use 294GB of Disk space and previews are 335gb of disk space.
By storing the catalogue and smart previews on Dropbox I can also use my laptop on the same catalogue for most things.
regards
Mark