It's easy. You use two pint pots.
I've been buying new, more powerful servers. I have four 2U servers, and a 1U. The servers are, in order of power:
Dell Poweredge R805
Dell Poweredge 2950
Dell Poweredge 2850
Dell Poweredge 2550
Dell Poweredge 1550
So first, the R805, vintage 2008. It came with twin Opterons, 64gb ram and two power supplies. I took out one of the power supplies (it's only useful to have two when you have two independent power sources). It didn't have any hard drives, so I put in a 64gb SD card as the system drive, because it has an SD card slot inside the server. I installed Fedora 23 on it, and some hard drives. There's three 3tb drives I had on the shelf, and two 4tb drives. That gives me 17 tb, enough space for all the customer data, plus room for expansion; the drives are about half full.
The expansion slots are PCI-E, but I'm used to using PCI. But a while ago, I accidentally bought a couple of PCI-E 4-port sata adaptors, so I used one of those, and it worked fine.
But the problem was, there isn't anywhere in the R805 that you can put five drives. It's the "quart in a pint pot" problem. I solved it by using a 1U case, with its power supply, and put the drives in that. The sata cables come out of the rear of the R805, and into the rear of the 1U case. It works well.
This is the computer that I intend to be customer-facing.
The second was the 2950, vintage 2006. I have to say, I like this computer, I like it a lot. It's very well designed. It came with twin Xeons and 16gb of memory, I upgraded it to 32gb, because I think that this will make it really fast. It also uses PCI-E. Again, I took out the extra power supply, and all the drives except two, which will be the Raid 1 (mirrored) system drive. Then I put in four 2tb drives and two 4tb in a separate 1U box - 16 tb. It has Fedora 24, 64 bit version.
The way I've got it arranged, the sata cables (m-m) come out of the rear of the 2950. The add-on 1U box has m-f sata cables coming out. So all I have to do is connect the sata cables to each other for it to work, and if I want to move the boxes separately, I just unplug those cables. It's not pretty, but it works nicely.
This computer is intended to be a backup to the first one - if anything goes wrong with the R805, I can quickly switch over to the 2950.
Then the 2850, vintage 2005. That's a bit older, and uses PCI cards, so I was able to use my usual sata adaptors. I gave it 8 2tb drives that I had on the shelf giving it 16tb, running off two sata adaptors. It came with twin Xeons and 3gb memory, I upgraded it to 16gb, which is as high as it will go. It's using Fedora 24, 32 bit version, because the processors are 32 bit.
This computer is intended to be the second backup to the R805. I like having two backups, because if you only have one backup computer, and the main machine fails, then you run your backup and cross your fingers that it doesn't fail because when you only have ne backup, then at that point you don't have a backup!
Then the 1550, vintage 2001, the 1U box. That came with 1gb, I upgraded it to 2gb. This uses the old Pentium III, but there's two of them. It's a lot slower compared to the other three, but it's still fast compared to what I've been using. It only has one power supply and I configured its two drives as a Raid 1 mirror, to act as the system drive. Then I added a 1U box to hold two 4tbs, a 2tb, 3 1tbs and two 0.5 tbs giving a total of 14tb and installed Fedora 24, 32 bit version. This is scraping the bottom of the barrel! Still, it's enough to hold all the customer data. My plan is that this box will never be customer-facing.
The final box is the 2550, vintage 2001. If came with two power supplies (I took one out), and installed Fedora 24, 32 bit version. There's no big drives; it's just sitting in reserve. If one of the others goes pear-shaped, I can bring this box into use.
The five servers cost me a tad over £100. And that's why I'm not using boxes made in 2016.