//cdfs3> info

Ctl   Model        Ports   Drives   Units   NotOpt   RRate   VRate   BBU
------------------------------------------------------------------------
c0    9650SE-8LPML 8       8        2       1        4       4       -        

//cdfs3> info c0

Unit  UnitType  Status         %Cmpl  Stripe  Size(GB)  Cache  AVerify  IgnECC
------------------------------------------------------------------------------
u0    RAID-5    OK             -      64K     1396.95   ON     OFF      OFF      
u1    RAID-5    DEGRADED       -      64K     1396.95   OFF    OFF      OFF      

Port   Status           Unit   Size        Blocks        Serial
---------------------------------------------------------------
p0     OK               u0     465.76 GB   976773168     WD-WCANU1137212     
p1     OK               u0     465.76 GB   976773168     WD-WCANU1090078     
p2     OK               u0     465.76 GB   976773168     WD-WCANU1119743     
p3     OK               u0     465.76 GB   976773168     WD-WCANU1089924     
p4     OK               u1     465.76 GB   976773168     WD-WCANU1136981     
p5     OK               u1     465.76 GB   976773168     WD-WCANU1109927     
p6     DEVICE-ERROR     u1     465.76 GB   976773168     WD-WCANU1069353     
p7     OK               u1     465.76 GB   976773168     WD-WCANU1125288     

Took out disk p6 and replaced with a new one. Waited a minute or so and got:

//cdfs3> info c0

Unit  UnitType  Status         %Cmpl  Stripe  Size(GB)  Cache  AVerify  IgnECC
------------------------------------------------------------------------------
u0    RAID-5    OK             -      64K     1396.95   ON     OFF      OFF      
u1    RAID-5    DEGRADED       -      64K     1396.95   OFF    OFF      OFF      

Port   Status           Unit   Size        Blocks        Serial
---------------------------------------------------------------
p0     OK               u0     465.76 GB   976773168     WD-WCANU1137212     
p1     OK               u0     465.76 GB   976773168     WD-WCANU1090078     
p2     OK               u0     465.76 GB   976773168     WD-WCANU1119743     
p3     OK               u0     465.76 GB   976773168     WD-WCANU1089924     
p4     OK               u1     465.76 GB   976773168     WD-WCANU1136981     
p5     OK               u1     465.76 GB   976773168     WD-WCANU1109927     
p6     OK               -      465.76 GB   976773168     WD-WCAPW5103756     
p7     OK               u1     465.76 GB   976773168     WD-WCANU1125288     

//cdfs3> /c0/u1 start rebuild disk=6
Sending rebuild start request to /c0/u1 on 1 disk(s) [6] ... Done.


//cdfs3> info c0

Unit  UnitType  Status         %Cmpl  Stripe  Size(GB)  Cache  AVerify  IgnECC
------------------------------------------------------------------------------
u0    RAID-5    OK             -      64K     1396.95   ON     OFF      OFF      
u1    RAID-5    REBUILDING     0      64K     1396.95   OFF    OFF      OFF      

Port   Status           Unit   Size        Blocks        Serial
---------------------------------------------------------------
p0     OK               u0     465.76 GB   976773168     WD-WCANU1137212     
p1     OK               u0     465.76 GB   976773168     WD-WCANU1090078     
p2     OK               u0     465.76 GB   976773168     WD-WCANU1119743     
p3     OK               u0     465.76 GB   976773168     WD-WCANU1089924     
p4     OK               u1     465.76 GB   976773168     WD-WCANU1136981     
p5     OK               u1     465.76 GB   976773168     WD-WCANU1109927     
p6     DEGRADED         u1     465.76 GB   976773168     WD-WCAPW5103756     
p7     OK               u1     465.76 GB   976773168     WD-WCANU1125288     

Now just need to wait for the rebuild to finish.