Variable speed recording method and apparatus for a magnetic tape drive

Abstract

A method and apparatus for varying track recording speed to maximize host-to-tape data transfer rates is presented. Variable data transfer rates of host systems and networks are accommodated by continually adjusting the tape speed to match the tape drive to the host's actual transfer rate. jThe speed of the tape is adjusted according to both the level of data present in the tape drive data buffer and whether the current mode of the drive is write mode or read mode. In the preferred embodiment, when the tape speed is accelerated or decelerated while writing a number of data track pairs to tape, a predetermined number of dummy track pairs are first written to tape at the current speed. On the next write head phase after the speed is increased or decreased as appropriate while the read heads are over the track, a predetermined number of dummy track pairs followed by more data track pairs are written to the tape at the new speed.

What is claimed is:  
     
         1 . A method for recording data at variable speeds onto a magnetic tape that is being transported across a rotating drum at a current tape transport speed, said rotating drum having a recording head disposed thereon to pass over said tape once per single rotation of said drum, said data being received from a host system and temporarily stored in a data buffer, said method comprising: 
 monitoring a current buffer level of said data buffer, said current buffer level indicating an amount of data currently present in said data buffer;    determining a new tape transport speed based on said current buffer level; and    adjusting said current tape transport speed to said new tape transport speed;    wherein said current tape transport speed and said new tape transport speed are each non-zero.    
     
     
         2 . A method in accordance with  claim 1 , comprising: 
 recording a track onto said magnetic tape at said new tape transport speed.    
     
     
         3 . A method in accordance with  claim 2 , wherein: 
 said recording step comprises: 
 recording a first set of tracks onto said tape at said current tape transport speed prior to adjusting said current tape transport speed to said new tape transport speed; and  
 recording a second set of tracks onto said tape after said current tape transport speed has been adjusted to said new tape transport speed.  
   
     
     
         4 . A method in accordance with  claim 3 , wherein: 
 said first set of tracks comprises a first data track, said first data track comprising a first set of said data in said data buffer that has been formatted into said first data track; and    said second set of tracks comprises a second data track, said second data track comprising a second set of said data in said data buffer that has been formatted into said second data track.    
     
     
         5 . A method in accordance with  claim 3 , wherein: 
 said first set of tracks comprises a first predetermined number of dummy tracks; and    said second set of tracks comprises a second predetermined number of dummy tracks.    
     
     
         6 . A method in accordance with  claim 3 , wherein: 
 said first set of tracks comprises a first data track followed by a first predetermined number of dummy tracks, said first data track comprising a first set of data in said data buffer that has been formatted into said first data track; and    said second set of tracks comprises a second data track followed by a second predetermined number of dummy tracks, said second data track comprising a second set of data in said data buffer that has been formatted into said second data track.    
     
     
         7 . A method in accordance with  claim 1 , wherein said new tape transport speed is slower than said current tape transport speed.  
     
     
         8 . A method in accordance with  claim 1 , wherein: 
 said new tape transport speed is faster than said current tape transport speed.    
     
     
         9 . A method in accordance with  claim 2 , comprising: 
 measuring said current tape transport speed;    determining whether said current tape transport speed is outside a speed control limit; and    if said current tape transport speed is outside said speed control limit, performing the steps of: 
 setting said new tape transport speed to a speed within said speed control limit;  
 adjusting said current tape transport speed to said new tape transport speed; and  
 re-recording said track onto said magnetic tape at said new tape transport speed.  
   
     
     
         10 . A method in accordance with  claim 2 , comprising: 
 measuring a track pitch, said track pitch comprising the distance between said recorded track and an immediately-previous previously-recorded track;    determining whether said track pitch is outside a track pitch control limit; and    if said track pitch is outside said track pitch control limit, performing the steps of: 
 setting said new tape transport speed to a speed that will place a next measured track pitch within said track pitch control limit;  
 adjusting said current tape transport speed to said new tape transport speed; and  
 re-recording said track onto said magnetic tape at said new tape transport speed.  
   
     
     
         11 . A method in accordance with  claim 1 , wherein: 
 said adjusting step comprises: 
 commencing said speed adjustment when said rotating drum is positioned such that said recording head is not positioned over said tape; and  
 completing said speed adjustment before said recording head becomes positioned over said tape.  
   
     
     
         12 . A method in accordance with  claim 2 , comprising: 
 reading back said recorded track at said new tape transport speed immediately after said recorded track is recorded onto said magnetic tape.    
     
     
         13 . A method in accordance with  claim 12 , comprising: 
 re-recording said track if said recorded track is unreadable.    
     
     
         14 . A method in accordance with  claim 1 , comprising: 
 reading a track from said magnetic tape at said new speed.    
     
     
         15 . A method for recording data at variable speeds onto a magnetic tape that is being transported across a rotating drum at a first tape transport speed, said rotating drum having a recording head disposed thereon to pass over said tape once per single rotation of said drum, said data being received from a host system and temporarily stored in a data buffer, said method comprising: 
 halting tape transport such that a current tape transport speed is reduced to zero;    monitoring a current buffer level of said data buffer, said current buffer level indicating an amount of data currently present in said data buffer;    determining a second tape transport speed based on said current buffer level, said second tape transport speed being non-zero; and    adjusting said current tape transport speed from zero to said second tape transport speed to commence tape transport.    
     
     
         16 . A method in accordance with  claim 15 , comprising: 
 recording a track onto said magnetic tape at said second tape transport speed.    
     
     
         17 . A method in accordance with  claim 16 , wherein: 
 said recording step comprises: 
 recording a first set of tracks onto said tape at said first tape transport speed prior to adjusting said current tape transport speed to said second tape transport speed; and  
 recording a second set of tracks onto said tape after said current tape transport speed has been adjusted to said second tape transport speed.  
   
     
     
         18 . A method in accordance with  claim 17 , wherein: 
 said first set of tracks comprises a first data track, said first data track comprising a first set of said data in said data buffer that has been formatted into said first data track; and    said second set of tracks comprises a second data track, said second data track comprising a second set of said data in said data buffer that has been formatted into said second data track.    
     
     
         19 . A method in accordance with  claim 17 , wherein: 
 said first set of tracks comprises a first predetermined number of dummy tracks; and    said second set of tracks comprises a second predetermined number of dummy tracks.    
     
     
         20 . A method in accordance with  claim 17 , wherein: 
 said first set of tracks comprises a first data track followed by a first predetermined number of dummy tracks, said first data track comprising a first set of data in said data buffer that has been formatted into said first data track; and    said second set of tracks comprises a second data track followed by a second predetermined number of dummy tracks, said second data track comprising a second set of data in said data buffer that has been formatted into said second data track.    
     
     
         21 . A method in accordance with  claim 15 , wherein: 
 said first tape transport speed is identical to said second tape transport speed.    
     
     
         22 . A method in accordance with  claim 15 , wherein said second tape transport speed is slower than said first tape transport speed.  
     
     
         23 . A method in accordance with  claim 15 , wherein: 
 said second tape transport speed is faster than said first tape transport speed.    
     
     
         24 . A method in accordance with  claim 16 , comprising: 
 measuring said current tape transport speed;    determining whether said current tape transport speed is outside a speed control limit; and    if said current tape transport speed is outside said speed control limit, performing the steps of: 
 setting a third tape transport speed to a speed within said speed control limit;  
 adjusting said current tape transport speed to said third tape transport speed; and  
 re-recording said track onto said magnetic tape at said third tape transport speed.  
   
     
     
         25 . A method in accordance with  claim 16 , comprising: 
 measuring a track pitch, said track pitch comprising the distance between said recorded track and an immediately-previous previously-recorded track;    determining whether said track pitch is outside a track pitch control limit; and    if said track pitch is outside said track pitch control limit, performing the steps of: 
 setting a third tape transport speed to a speed that will place a next measured track pitch within said track pitch control limit;  
 adjusting said current tape transport speed to said third tape transport speed; and  
 re-recording said track onto said magnetic tape at said third tape transport speed.  
   
     
     
         26 . A method in accordance with  claim 15 , wherein: 
 said adjusting step comprises: 
 commencing said speed adjustment when said rotating drum is positioned such that said recording head is not positioned over said tape; and  
 completing said speed adjustment before said recording head becomes positioned over said tape.  
   
     
     
         27 . A method in accordance with  claim 16 , comprising: 
 reading back said recorded track at said second tape transport speed immediately after said recorded track is recorded onto said magnetic tape.    
     
     
         28 . A method in accordance with  claim 26 , comprising: 
 re-recording said track if said recorded track is unreadable.    
     
     
         29 . A method in accordance with  claim 15 , comprising: 
 reading a track from said magnetic tape at said second speed.    
     
     
         30 . A reel tension controller for a tape transport mechanism, said tape transport mechanism comprising a capstan which controls tape transport, a supply reel and a takeup reel between which a magnetic tape is transported, comprising: 
 a reel amplifier responsive to a reel amplifier input signal to adjust the tension between said capstan and said supply reel and said takeup reel;    a controller responsive to correct tension parameters, a supply reel radius signal, and a takeup reel radius signal, said controller generating said reel amplifier input signal based on said correct tension parameter, said supply reel radius signal and said takeup reel radius signal.    
     
     
         31 . A method for preventing the recording of a thin track on a magnetic medium by a magnetic tape drive, said magnetic tape drive comprising a tape transport mechanism comprising a supply reel, a takeup reel, a recording head, and a capstan which moves a magnetic tape between said supply reel and said takeup reel in a path across said recording head, said capstan comprising a capstan tachometer which maintains a capstan tach count proportional to a number of revolutions of said capstan that have occurred relative to a beginning-of-tape position of said magnetic tape in said drive, said method comprising the steps of: 
 determining a reference position of a track based upon a current tape speed;    measuring a current position of said track based upon said current tach count of said capstan;    determining a current track spacing, said current track spacing comprising the distance between a first track and a second adjacent track;    calculating a current track spacing error from said reference position and said current position; and    if said current track spacing error is below an acceptable track spacing error threshold: 
 setting said reference position to said current position;  
 setting said current track spacing error to zero.  
   
     
     
         32 . A method in accordance with claim  31 , comprising the step of: 
 repeating each of said steps periodically.