I have had my ups and downs with two of these machines purchased in January.  I set them up with two 1TB Samsung EVO 2.5 inch SATA SSDs in a RAID 1 array.  This turned out to be a huge mistake.  One of the machines quit working in May.  I later learned that the SATA RAID controller on the Z620 motherboard can't handle SSDs in a RAID. The controller destroyed both SSDs at the same time in matter of months.To regain the reliability RAID 1 offers my business, I ordered two new Z4 G4 workstations from HP with Enterprise SSDs factory installed in a RAID 1 array.  They will arrive in month or two.  I'm sure the RAID controller in them will be able to handle the SSDs.  But do I really need RAID 1?  My data files are already  protected in a NAS with its own RAID set up with conventional HDDs that are fast enough, and they are backed up another remote NAS nightly.  But, it takes several days to reinstall dozens of programs and fully recover from a crashed boot drive.  So RAID 1 is essential for my business.Meanwhile, I set the Z620s up to boot WIN 10 from single NVME SSDs mounted on a PCIE3.0 card using a boot manager, REFIND, installed on a USB thumb drive.  Wow!  They are now blazing fast. The old machines are now much faster than the new replacements will be when they are delivered.  I wish I had not spent the money to equip them with Enterprise SATA SSDs.  I can install aftermarket twin NVME SSDs mounted on a PCIE4.0 card with a RAID controller built into the card for half as much and get more than triple the speed.  I can't do this with the Z620s because their motherboards do not support "PCIE Bifurcation," which is needed to set up multiple PCIE mounted SSDs in a RAID array.  But they will be terrific for less critical personal uses, like photo and video editing.