Storage: How many drives can be stuffed in a Box?

How many 2.5" drives can be stuffed into a single enclosure, allowing space for power, cooling, wiring and a single motherboard? Short answer: ~500-1000.

This assumes drives mounted vertically, thin side forward, needing 105-110mm vertically and ~75mm deep per drive. Drives are mounted on a carrier, secured in a slide, vertically is assumed.

Drives can be mounted in a single row on a carrier, or dual rows of drives per-carrier, back-to-back. This may have advantages in construction and widening air-flow gaps. Testing needed to show if vibration isolation needed.

Extra drives can be mounted horizontally in the free space. As well, drive carriers can be oriented alternately horizontally and vertically, lowering coupling of vibration between adjacent groups.

Drives will fit in a 3RU (133mm) enclosure, requiring space behind the drives for PSU's, fans and motherboard, or in 4RU (177mm), allowing 1.5RU underneath drives for electronics & wiring.

In a 42RU high rack, there is space for 14x3RU enclosures or 10x4RU enclosures.
These calculations ignore limitations of weight and power imposed by floor loading and racks.
 9000 drives at 0.1kg each is 900kg.
At 1W/drive, 9kW power used.

Count depends on:

• The thickness (5mm-15mm) of drives used: from 76 to 25, with 40 for maximum platters.
• How deep drives are stacked. @ 75mm/drive this is:
• 450mm = 6 drives deep
• 600mm = 8 deep [in 3RU, allows electronics behind]
• 900mm = 12 deep [in 4RU, forces electronics underneath]

Totals are:

• 3RU, Max HDD (5mm) =  8 x 76 = 608/enclosure [300TB] = 8,512/rack @ 0.5TB/HDD
• 4RU, Max HDD (5mm) = 12 x 76 = 912/enclosure [450TB] = 9,120/rack

• 3RU, Max Platters (9.5mm) =  8 x 40 = 320/enclosure [320TB] = 4,480/rack @ 1TB/HDD
• 4RU, Max Platters (9.5mm) = 12 x 40 = 480/enclosure [480TB] = 4,800/rack

• 3RU, Max Cap drive (15mm) =   8 x 25 = 200/enclosure [400TB] = 2,800/rack @ 2TB/HDD
• 4RU, Max  Cap drive (15mm) = 12 x 25 = 300/enclosure [600TB] = 3,000/rack

Previous pieces on Storage with 2.5" drives:

• http://stevej-lab-notes.blogspot.com.au/2014/03/storage-more-capacity-calculations.html
• http://stevej-lab-notes.blogspot.com.au/2014/03/storage-efficiency-measures.html

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Table of 2.5" Platter equivalent across 19" Rack

Rack Width: 435mm (17.125in, allows for sliders)
Interdrive space (cooling): 52.5mm
Usable space: 382.5mm
1 Rack Unit: 1.75 in or  44.45mm (Clearance of 0.5mm = 44 mm usable)
3 Rack Unit: 5.25 in or 133.35mm (Clearance of 0.5mm = 132.75 mm usable)

4 Rack Unit: 7.00 in or 177.80mm (Clearance of 0.5mm = 177 mm usable)

Drive thickness	Count across Rack	Platters
15mm	25	100
9.5mm	40	120
7mm	54	108
5mm	76	76

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