This answer differs by system Generation.  

Generation 9:  All Generation 9 appliances ship with included Rail Kits for standard racks.  Alternate Rail Kits are available for Full Rack Depth Gen 9 appliances as noted in the chart below.  Rail systems for Generation 9 appliances can be acquired directly from Dell or Dell resellers. 

Half Rack Generation 9

These units include Dell A4 static rails compatible with center mount 2 post racks or standard 4 post racks. 

1U Full Rack Depth

These systems come with Dell A11 Stab-in sliding Ready Rails for 4 post standard racks.  An optional cable management kit is available from Dell direct or Dell resellers for this kit (it not sold by Unitrends)

2U Systems

These systems come with Dell B6 Stab-in Sliding Ready Rails for 4 post standard racks.  An optional cable management kit is available from Dell direct or Dell resellers for this kit (it not sold by Unitrends)

For more information about racking requirements for Generation 9 systems, locate the current Site Preparation Guide on our Documentation Site.  

Generation 7 and 8:  

Half Rack Class: (6xx or 8002-8012)

These systems do not come with rail kits.  These appliances mount to racks using the included rack "ears" and should be stabilized on a rack shelf.  An optional traditional rail kit is available from SuperMicro and can be purchased through numerous vendors, but is not carried by Unitrends.  

Full Rack Class (1U or larger)

These come with standard depth square-hole standard rack rails.  These rail kits are compatible with universal 4 post square-hole racks of expected depths.  Alternative rail kits to conform to racks that do not meet the stated mounting requirements conveyed in the 10.0 edition of the site preparation guide may be available from SuperMicro directly for some chassis models for additional purchase from 3rd party.  Unitrends does not sell optional rail kits for other racks, but some options for Generation 7, or 8 units are noted below that may be available.   These units are not supported in 2 post racks.  

Optional Rail Kits by Chassis model for Generation 7, 8, and 9 appliances:  

Note: These are not carried by Unitrends, but are noted by the chassis manufacturer as optional compatible equipment.  These typically provide support for alternative depth 4 post square hole racks.  Current generation appliances may not be compatible with non-standard or vendor proprietary racks.  

If you are unable to locate suitable rails for your 3rd party rack:  You may use a certified/approved rack shelf rated for not less than the Unitrends Appliance listed weight support designed for your non-standard rack.  

Warning:  Do not stack other equipment or servers on top of a mounted Unitrends appliance, the rails are rated ONLY for the listed weight of the appliance and must not support additional equipment placed above.    

For older generation appliances, see the Site preparation Guide that was shipped with your appliance release and reference the Chassis Number for your model.  If you cannot locate this guide or have an older chassis not listed here covered by an active support contract, please contact Unitrends support and we can look that information up for you.  Again, Unitrends does not directly sell alternate rail kits, you will need to contact a 3rd party reseller to acquire those components.