The CACHE command

Use the undocumented switch 

  /WRITECACHE:size_in_bytes 

of the <CACHE command to specify the maximum size of writes to be cached. 
The default value for this parameter is 65,536; the maximum is also 
65,536. 

Source:  The OS/2 WARP Survival Guide 

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 Use the undocumented switch /Dstg:on to get some more information and 
 switches for CACHE.EXE. Use 

  
   CACHE /Dstg:on /?
 

 to get a syntax help for the undocumented switches. 

 (WARP 4 only! but the switches /DirtyMax:n and /Writecache:n also work in 
 WARP) 

 Source:  Team OS/2 WEB pages