Input Processing Output I I I I Initialize tracks.
2 Format and write track O. I :> 3 If requested, write the IPL program.
4 Format and write the
standard Volume Table of Initialized Virtual Disk Contents. Notes Module Label Ref Notes Module Label Ref 1 When the defective flag test is IBCDASDI INTALT 3 The user-supplied IPL initialization IBCDASDI WRTIPL suppressed, the home address is program is written. The program is
written followed by a maximum written on cylinder 0 track 0 or 1, or, length record 0 consisting of if the track is defective, on its
hexadecimal 55. The track is read assigned alternate.
and checked. A maximum·length I record 0 is written again, this time I I I consisting of hexadecimal 00. The I track is again read and checked. If a
data check is encountered, this I write sequence is repeated ten times. I 4 The DSCBs needed for the VTOe l,seDASDI r- ... IIT\/Tn,... rIVIIVIV,,", I are constructed: the DSCB (format 4)
and the DADSM DSCB (format 5). For the 3330 series, the alternate
track field in the format 4 DSCB is set to zero since no alternate If data errors still occur, the track is track cylinder is provided. Then, the
flagged as defective. An alternate VTOC is written at the user-specified WRTVTOC track is assigned when the device is location and normal end of job is
disk. For drum devices, a message is initiated. Control returns to CPo issued indicating the address of the
defective track. IBC10l1 BAD TRACK cccehhhh If the home address-record 0 area is
defective on a 2314 or 2319 disk
storage volume, an attempt is made
to move the home address-record 0 fields down the track approximately 800 bytes.
2 Track 0 is written. It consists IBCDASDI CONSTR2 I ;of two IPL records (or a dummy !PL record), a standard volume label and
up to seven additional labels. l Diagram 1-2. Initializing a Virtual Disk
Chapter 1. IBCDASDI--The Virtual Disk Initializaticn Program

Input Processing Output Notes 1 If the track bypass is not selected,
a track check is performed on the
user-specified track. If the track is good, a message is issued. IBC1091 TRACK CHK INDICATES
TRACK IS GOOD 2 The ASGNALT routine flags the given
track as defective and assigns an
alternate. If the defective track is a
primary track, the primary track is
flagged and an alternate track is
assigned. If the defective track is an
alternate track that was not assigned
to a primary track, the alternate
track is flagged as defective. However,
if the defective track is an alternate
track that was assigned to a primary track, the alternate track is flagged and
another alternate is assigned to the
primary. Then, the TRKPRNT routine causes
a message to be printed stating the
address of the defective track and its
assigned alternate. IBCllOI BAD TRACK cccchhhh IBCllll ALTERNATE cccchhhh
3 Field six of the VTOC is decremented
to indicate that one less alternate
track is available, field five is
incremented to point to the next available alternate track.
Module IBCDASDI IBCDASDI IBCDASDI If specified, track check is
performed.
2 Flag defective track, assign
alternate.
3 Update the VTOC. Label Ref Notes ) GETALTX Control is then given to location
GETAL T to repeat the process for
GETALT2 the next user-specified track, or, if
none exists, to initiate normal
end of job. Control returns to CPo ASGNALT
TRKPRNT
GETALT4
Diagram 1-3. Assigning Alternate Tracks
8 IBM VM/370 Service Routines Program Logic 8 VTOC Module Label Ref