SCF Reference Manual for the Storage Subsystem (G06.27+, H06.04+)

Managing Magnetic Disks
SCF Reference Manual for the Storage Subsystem—529937-008
7-14
Sparing a Defective Sector
Sparing a Defective Sector
Sector sparing is the process of moving the data on a physically defective sector to a
different sector and preventing data from using that defective sector again. A disk
sector can be spared in two ways:
•
Enabling Automatic Sector Reallocation on page 7-14
•
Sparing a Sector Manually on page 7-15
Automatic Sector Reallocation
If automatic sector reallocation is enabled (the default), the system automatically
spares defective disk sectors when detected. The INFO, LOG command displays
spared sectors.
Automatic sector reallocation is controlled by the $ZRD9 process. This generic
process starts automatically when you load the system and continuously searches for
media error events on every sector on every disk in the system.
When automatic sector reallocation finds a media error event, it starts the $ZARS
process. $ZARS spares the bad sector, updates the system’s internal database, and
continues to run as long as media error events are reported. When no more media
error events are reported, $ZARS stops.
Displaying Information About Automatic Sector Reallocation
To determine whether automatic sector reallocation is enabled on your system, at the
TACL prompt:
> STATUS $ZRD9
Enabling Automatic Sector Reallocation
To enable automatic sector reallocation:
-> START PROCESS $ZZKRN.#ROUTING-DIST
Disabling Automatic Sector Reallocation
If you want to disable automatic sector reallocation, you must disable it for all disks;
you cannot enable or disable it for specific disks.
System \COMM
Process Pri PFR %WT Userid Program file Hometerm
$ZRD9 0,381 150 015 255,255 $SYSTEM.SYS00.EMSDIST $ZHOME
Swap File Name: $SYSTEM.#0
Current Extended Swap File Name: $SYSTEM.#0
$ZRD9 B 1,372 150 001 255,255 $SYSTEM.SYS00.EMSDIST $ZHOME
Swap File Name: $SYSTEM.#0
Current Extended Swap File Name: $SYSTEM.#0