Working with DASDs in a copy-pair relation

6.10 LPAR mode z/VM guest KVM guest

Control the copy relation of DASD devices on Linux with sysfs attributes.

Before you begin

To set up a copy-pair relationship, the secondary device must be offline while the primary device can be online or offline.

About this task

DASDs can be set up in a copy-pair relationship using, for example, Peer-to Peer- Remote-Copy (PPRC). A pair consists of a primary volume and a secondary volume. Data written to the primary volume is replicated on the secondary volume by the storage system.

This task describes how to set up a copy-pair relation on Linux. It will not set up the storage server. Find out what the copy-pairs are from your storage server and match them in Linux.

You can control the copy-pair relationship of a DASD with the copy_pair and copy_role sysfs attributes. You can use primary DASDs as ordinary block devices, but you cannot directly access secondary devices.

Procedure

To query the copy role of a device, read from the copy_role sysfs attribute.
Possible values are:

none

Not part of a copy relation or no copy relation has been set up.

primary

The device is the primary device in a copy relation.

secondary

The device is the secondary device in a copy relation.
For example, to query the copy-pair role of a DASD with the device bus-ID 0.0.9700, issue:
```
# cat /sys/bus/ccw/devices/0.0.9700/copy_role
primary
```
The example shows that DASD 0.0.9700 is a primary device.
To add a copy-pair, issue a command of this form:
```
# echo <primary_bus_ID>,<secondary_bus_ID> > /sys/bus/ccw/devices/<bus_ID>/copy_pair
```
Where:

<primary_bus_ID>

is the device bus-ID of the primary DASD device.

<secondary_bus_ID>

is the device bus-ID of the secondary DASD device.

<bus_ID>

is the device bus-ID of either the primary or secondary DASD device; the relationship is set up for both devices.
For example, to add a copy pair with primary device 0.0.9700 and secondary device 0.0.9740, issue:
```
# echo 0.0.9700,0.0.9740 > /sys/bus/ccw/devices/0.0.9700/copy_pair
```
For multiple secondary device, repeat the setup for each pair. Cascading secondary devices are not supported. If a mismatch is detected, the devices cannot be set online.

To delete all copy-pairs for a device, issue a command of this form:

# echo clear > /sys/bus/ccw/devices/<bus_ID>/copy_pair

All relations are deleted on the device with bus_ID and all associated devices.

For example:

# cat /sys/bus/ccw/devices/0.0.9700/copy_pair
0.0.9700,0.0.9740
# echo clear > /sys/bus/ccw/devices/0.0.9700/copy_pair
# cat /sys/bus/ccw/devices/0.0.9700/copy_pair
# cat /sys/bus/ccw/devices/0.0.9740/copy_pair