Checking for access by other operating system instances

6.10 LPAR mode z/VM guest KVM guest

Query if a DASD volume is online to another operating system instance by reading the host_access_count attribute.

Before you begin

To query the number of operating system instances that use the DASD device, the DASD must be online.

About this task

Storage servers that support this feature know about the online status of the device on all attached operating system instances in an LPAR (so called hosts). If a DASD device is set online it might potentially be used on another operating system instance. This information can help to reduce the chance for outages or possible data corruption due to concurrent access to DASD volumes from different operating system instances.

Procedure

To check whether a DASD device is being used by other operating system instances, issue a command of this form:

# cat /sys/bus/ccw/devices/<device_bus_id>/host_access_count

where /sys/bus/ccw/devices/<device_bus_id> represents the device in sysfs.

For example, to query how many operating system instances have access to a device 0.0.bf45, issue:

# cat /sys/bus/ccw/devices/0.0.bf45/host_access_count
13

In the example, 13 operating system instances have access to the device, including the current Linux® instance.

What to do next

To see details for each host connected to the DASD device, use the lsdasd command with the --host-access-list option. For more information and an example, see lsdasd - List DASD devices.