The options with dell part numbers are at

https://www.dell.com/support/kbdoc/en-uk/000146243/upgrading-storage-in-the-dell-precision-5820-7820-7920-tower-workstations

If you're happy with internal bays, you might want to consider the internal Flex 3 & Flex 4 spaces

Bit confused I want all my bays to be internal for now just looking to populate top front bay where dvd use to be and Flex 3 & Flex 4 spaces that’s in the back right ? And on link I can’t find front bay hardware part or number 

thanks 

If you look in the document for Dell parts 400-AXBM and 400-AXBJ 

400-AXBM - Allows user to install one 3.5" hard drive into the 5.25" bay when using the embedded storage controller only. These drives would be internally accessible only.

400-AXBJ - Allows user to install two 2.5" HDD/SSDs into the 5.25" bay when using the embedded Intel Storage controller only. This module fits into the place where a standard Half Height optical drive (CD or DVD) would fit in the system. These drives would be internally accessible only.

That's the 'official' Dell way but, assuming you're already out of warranty, there's nothing stopping you using 3rd party 5.25" to 3.5" (or 2 x 2.5") adapters and DIYing it. Just make sure you're happy that the drives aren't going to overheat - a lot will depend on the type of drive and how heavily they're going to be used.

And, yes, the Flex 3 & 4 are at the rear, look in the document for 575-BBSI

575-BBSI - Allows user to install 4 additional 2.5" or 3.5" SATA hard drive/SSDs on the Rear of the chassis in FlexBay 3 and 4.

Again, it's quite possible to create your own DIY mounting solution for these bays

@PapaPee​ 

Thanks for all the info you diy route I any suggestion ? What cable would I need to connect few hard drives internally would you know ? 

For the 5.25" bay, I used https://www.amazon.co.uk/dp/B0CLGR8NJZ to mount a 3.5" HDD in a 5820, it wouldn't be difficult to use it to mount 2 x 2.5" SSD or similar (they're so light that double-sided tape keeps them in place). I didn't bother with a fan as I put in a 5400 rpm drive for bulk storage so it's not in constant use, I've kept an eye on temperatures and it only gets a few degrees above ambient.

You should find an additional SATA power cable and data cable in place and available for the bay and you could use a splitter to allow for two drives - a second data cable can be run from the motherboard SATA ports.

If trying to add lots of internal drives, you're likely to run out of SATA ports - it might be better to look at NVMe, the Dell Ultraspeed Quad PCIe card fits into a x16 slot (assuming you're not using twin video cards) , it's freely available on eBay and takes 4 NVMe drives. You can also add the dual version of the card (supports 2 x NVMe) in a x8 slot.

I've used both and they work very well - I've also added a single NVMe in a x4 slot using one of these https://www.amazon.co.uk/dp/B0CQZ6SYD1?th=1 and it works perfectly.

I forgot to add the link for a example SATA power splitter  https://www.amazon.co.uk/dp/B08ZSN5CGF

This will allow you to mount 2 x 2.5" and 1 x 3.5" drives into the DVD bay

https://www.amazon.co.uk/dp/B01N1P804G

And this will allow you to power 3 drives from one SATA power lead

https://www.amazon.co.uk/dp/B004HTHJWM

Just add some extra SATA data leads of the correct length

If you used a 5400rpm drive and 2 SSDs, power and heat shouldn't really be an issue but you should keep an eye on drive temperatures over the first few weeks to see if a fan is needed or not.

Hello,

if you want something that will keep the temperature down or  maximize the slot usage

ICY DOCK: Manufactures Removable SSD / HDD Data Storage Enclosures

@PapaPee​ 

Thanks for all the info super informative. I decided to run 2 ssd from the top 5.25 bay I will need power splitter but when it come to data cable  on the motherboard in the back not front it’s double plug at bottom believe cable for it is called  called HD Mini SAS to 4XSATA Cable my question is can I connect 2 ssd via this plug it’s basically one square plug then 3 normal flat esata cables going in to drives ?

@PapaPee​ 

I have 2 mvme 500 gb each that come with my Dell but would like to relocate the from front bays to internal card Inseem one you listed but it’s single I found this one on eBay Dell DPWC300 NVMe M.2 PCIe Solid State Storage Adapter Card any thought ? Thanks