Research
Hardware
Rack max depth ~500mm.
Dell PowerEdge R710
- Depth 681mm
 - £200-300 on eBay
 - PERC H800 external RAID card (dual miniSAS)
 - Or non-raid PCIe with dual miniSAS
 - lots of RAM
 -   CPUs? 
- X5650 > E5645 > E5620 > E5606 > E5507 > X5560 = X5550
 
 - power and thermal requirements?
 - PCIe expansion slots?
 - 2xGigE
 
Dell PowerEdge R210
- R210 II specs
 - Depth 390mm
 - HP Version of the R210 II is the DL320e Gen8 v2
 - 1x PCIe x16
 
HP DL320e G8 v2
- G8 v2 specs
 - Depth 381cm
 -   Requires railkit 
- 775612-B21 ordered via Amazon UK (~£68)
 
 - Single Xeon
 - 1U
 - Seems like G8 v1 was a full depth chassis
 - 2x PCIe (x8, x4)
 
HP DL20 G9
- Compact 1U
 - Too expensive?
 
Others
https://en.wikipedia.org/wiki/List_of_Dell_PowerEdge_Servers
- R610 (1U, 2.5" only)
 - R720 (Xeon E family, 768GB RAM, 4xGigE)
 
Storage adapter
- Dual miniSAS (SFF-8088)
 - PCIe
 - Dell H200 (internal only?, JBOD)
 - LSI-SAS 9207-8e (PCIe 8x, SFF-8088)
 - LSI-SAS 9200-8e (some IBM card cross-flashed?)
 
LSI LSI00138
- PCIe 8x
 - SAS only?