Looks like CentOS/7 is dead. I believe the last "real" update is the end of this year, with maintenance updates till 2024 or something. So I'm looking at upgrading to CentOS/8, and decided that why not just get new computer hardware with faster everything as well. So I'm looking at things anew.

My need will be to run virtualization, a couple Linux VMs, at least one Win/10: who knows what I'll add later.

In my old system I had RAID. CentOS/7 had a software RAID, I went with it for RAID-1. Emphasis on "INEXPENSIVE", I felt it didn't cost me much in time or speed to have an extra disk, and I was covered for the most common error: disk failure. Software RAID has flaws in recovering a bad disk (the back-up can mostly just be swapped, but the main one needs some hocus-pocus). If I go with it again, it'll be a hardware RAID.

QUESTION: At the time of my original purchase, SSD wasn't tested/used enough for me. But this time I'm thinking of going SSD instead of HD. What do y'all think?

There isn't really a need to RAID SSD as I'm not going to get a head-crash or something, or should I? I don't know how impolitely SSD fail.

My second question is virtual memory, aka "swap".
As I was reading up & thinking what to do differently this time, it seems the opinions are all over the map for how much virtual to have changes as the amount of real gets up there. And there was even opinion that it can be too big--getting in its own way, etc.

What do y'all think? What's y'all's rule of thumb?

CentOS/7 limited me on how much memory: both proper as well as secondarily: the size of the VMs. CentOS/8 was explicit in how it "solved" all those problems. My final question; as things keep expanding in size--it's been a while since I've built a new computer system--what's today's current rule-of-thumb of memory size?

RAM - as much as you can afford. 16G minimum these days I would reckon (for non VM use)
SSD - absolutely. And yes they too will fail.
Swap - I allocate 2G on every system, no matter how much the RAM - when I see it being used, I ask why. Can always be added dynamically.
RAID - I prefer software, then you're not tied to a specific manufacturer/chipset that may not be there when things break.

BACKUPs - RAID ain't a backup replacement.

hey syg00, thanks. Got lost, never got an email that a reply came in and forgot to check manually until today.

Yeah, in my current system, it's 16 GiB real, so my Linux VM has 6GiB, my Win/10 VM has 4GiB, leaving 4GiB for the main Linux running KVM.

My Linux made the "swap" about 3+ GiB. It's often used up entirely, and I'm not doing that much stuff, just lots of browser windows, VLM running audio or video. So I'm wondering to create more "virtual", and if so, is twice "real" a good figure? (This question is now moot, since I'm planning on replacing everything.)

I was going to have multiple flavors of Linux running when I started this so many years ago, but it got derailed, besides which the performance was poor enough that I'd run one or another, and rarely-rarely two simultaneously. Change of business plans ha ha ha

I was hoping the virtual in the "real" system running KVM would suffice, but it didn't.

(If)/When I try this again, I'll get enough memory to 10+GiB per planned VM.
And brings me back to: any advice/counsel/cautions of how relatively large for the Virtual Portion of each piece.

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Do I infer correctly you're comfortable to go completely SSD ?

And, yes, RAID isn't a replacement for back-up, which I do as well.
I was merely saying that a normal disk failure is the most common and it's easily remedied with RAID, emphasis on I(nexpensive).

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CentOS's software RAID, when I built the system, let the systems build itself, it made the first disk bootable, but not the second. So I could just swap out the second disk, and with a little hocus-pocus, it'd be recreated. It was a shock to find out the second disk was not bootable and that I'd have to do a lot of hocus-pocus BEFORE I could swap out the first/main disk. <.sigh>

I didn't pay that much attention when I built the system, but I'm sure it was just selecting whether I wanted software RAID or not, if I wanted LVM or not. I'm quite sure I neither did, or did NOT do something that caused my problem. BUT if you're happy with software RAID, SYG00, I'll look into that when I begin my research. Thanks.

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LVM, in case anyone cares, worked very well with Linux VM. Just allocate more disk space to that VM, then go to that VM and some very simple steps and that VM now knows there is more disk space and you want it part of this, that or a third new file system.

However, to Windows, it's a very complicated PowerShell rigamarole. I don't need much from windows, just an occasional thing, so I eventually just rebuilt a Windows VM with the disk and memory space I wanted.

(Since I'm here, on the OS/X, the VM package there, I just had to move a slider bar to fix both disk and memory -- not even a reboot ha ha ha)