Field IOBFLAGIIOBFLAG IIOBST1T IOBERP I IOBRSTRT I IOBFAT1L Action To Be performed by DMKIOS I I 1 I 0 I 0 Return control when solicited device end I I arrives I I 1 I 1 I 0 Restart using IOBRC1W I I 0 I 0 I 1 Permanent I/O error I I 0 I 0 I 0 Retry successful
Figure 22.Summary of lOB Indicators
If the error is uncorrectable or intervention is required, theERP calls DMKMSW to notify operator. The specific message is identified in
theHSGPARH field of the IOERBLOK.
ALTERNATE TRACKRECOVERY, ERP (DHKTRK)
The software alternate track recovery support described in the following
paragraphs applies only to the 3340/3344 disk. For 3330 and 3350 disks
no software support is needed since the hardwareperforms alternate
track recovery. No support is needed for the 2305 drum since the CE is
able to rewire the device to use spare tracks in place of defective
tracks. For the 2314 and 2319 disks no true alternate track recovery is
provided by CP. But track condition checksfrom any device type are
reflected back to the virtual machine. Therefore, even though CP itself
cannot use a 2314 or 2319 cylinder that contains a defective track, it
it possible for a virtual machine to use such a cylinder if it provides
itsown error recovery. To facilitate this, the VM/370 version of the
IBCD1SDIprogram allows 2314 and 2319 minidisks to be formatted with an
alternate track cylinder as the last cylinder of each ainidisk rather
than using the last cylinders of the real disk for this purpose.
The 3340 alternate track support applies to CP I/O, to DiagnoseI/O (thereby giving alternate track support to CMS), and to SIO executed in
a virtualmachine. For CP I/O and Diagnose I/O, the alternate track
recovery support essentially consists of directing (seeking) an
interrupted channel program to an alternate track and restarting it.
Later, insome cases, the interrupted channel program is directed back
to the original cylinder and restarted there. ForSIO in a virtual machine, the operating system in the virtual machine provides its own
error recovery when CP reflects a track condition check to the virtualmachine. On the 3340 disk, alternate tracks are assigned in the conventional
alternate tracks cylinders at the high end of the real disk, not in the
last cylinder of each ainidisk. Therefore a virtual machinemay need to
seek outside of itsainidisk extent. This occurs when an operating
system in a virtualmachine performs its own error recovery following a
track condition cbeck.So for SIO issued from a virtual machine, CP's 1-166 IBM VM/370 System Logic and Problem Deterlination--Volume 1
Figure 22.
If the error is uncorrectable or intervention is required, the
the
ALTERNATE TRACK
The software alternate track recovery support described in the following
paragraphs applies only to the 3340/3344 disk. For 3330 and 3350 disks
no software support is needed since the hardware
track recovery. No support is needed for the 2305 drum since the CE is
able to rewire the device to use spare tracks in place of defective
tracks. For the 2314 and 2319 disks no true alternate track recovery is
provided by CP. But track condition checks
reflected back to the virtual machine. Therefore, even though CP itself
cannot use a 2314 or 2319 cylinder that contains a defective track, it
it possible for a virtual machine to use such a cylinder if it provides
its
IBCD1SDI
alternate track cylinder as the last cylinder of each ainidisk rather
than using the last cylinders of the real disk for this purpose.
The 3340 alternate track support applies to CP I/O, to Diagnose
a virtual
recovery support essentially consists of directing (seeking) an
interrupted channel program to an alternate track and restarting it.
Later, in
to the original cylinder and restarted there. For
error recovery when CP reflects a track condition check to the virtual
alternate tracks cylinders at the high end of the real disk, not in the
last cylinder of each ainidisk. Therefore a virtual machine
seek outside of its
system in a virtual
track condition cbeck.