A drive bay is a standard area for adding hardware to a computer. Most drive bays are fixed to the inside of a case, but some can be removed.
HPE DL38X Gen10 8LFF Front 2NVMe HDD Bay Kit

HPE DL38X Gen10 8LFF Front 2NVMe HDD Bay Kit

Hewlett Packard Enterprise
£222.99
StarTech.com 4-Bay Backplane for U.2 Drives, Fits in a 5.25inch Bay, Quad-Bay Mobile Rack Enclosure for 2.5inch U.2 (SFF-8639) HDD/SSDs, Includes Mini-SAS HD Cables and Removeable Trays - Backplane with Fans

StarTech.com 4-Bay Backplane for U.2 Drives, Fits in a 5.25inch Bay, Quad-Bay Mobile Rack Enclosure for 2.5inch U.2 (SFF-8639) HDD/SSDs, Includes Mini-SAS HD Cables and Removeable Trays - Backplane with Fans

StarTech.com
£315.99
Intel A2U8X25S3DPDK2 drive bay panel 2.5

Intel A2U8X25S3DPDK2 drive bay panel 2.5" Carrier panel Black, Stainless steel

Intel
£168.99
Lenovo 7XH7A05906 drive bay panel 2.5

Lenovo 7XH7A05906 drive bay panel 2.5" I/O ports panel Green

Lenovo
£161.99
StarTech.com 2.5

StarTech.com 2.5" Hot Swap Hard Drive Tray

StarTech.com
£17.99
StarTech.com 5.25 to 3.5 Hard Drive Hot Swap Bay - For 3.5

StarTech.com 5.25 to 3.5 Hard Drive Hot Swap Bay - For 3.5" SATA/SAS Drives - Trayless - Aluminum

StarTech.com
£38.99
StarTech.com Dual-Bay 2.5” SATA SSD / HDD Rack for 3.5” Bay - Trayless - RAID

StarTech.com Dual-Bay 2.5” SATA SSD / HDD Rack for 3.5” Bay - Trayless - RAID

StarTech.com
£30.99
StarTech.com 2.5” to 3.5” SATA Aluminum Hard Drive Adapter Enclosure with SSD / HDD Height up to 12.5mm

StarTech.com 2.5” to 3.5” SATA Aluminum Hard Drive Adapter Enclosure with SSD / HDD Height up to 12.5mm

StarTech.com
£24.99
DELL RD1000 Black

DELL RD1000 Black

DELL
£148.99
Lindy SAS & SATA Backplane Black, Silver

Lindy SAS & SATA Backplane Black, Silver

Lindy
£18.99
HP Optical Bay HDD Mounting Bracket

HP Optical Bay HDD Mounting Bracket

HP
£81.99
HP DP25 Removable 2.5in HDD Spare Carrier

HP DP25 Removable 2.5in HDD Spare Carrier

HP
£147.99