Installation guide

Appendix A. The Device Mapper
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0 65536 striped 2 512 /dev/hda 0 /dev/hdb 0
A.1.3. The mirror Mapping Target
The mirror mapping target supports the mapping of a mirrored logical device. The format of a mirrored
target is as follows:
start length mirror log_type #logargs logarg1 ... logargN #devs device1 offset1 ... deviceN
offsetN
start
starting block in virtual device
length
length of this segment
log_type
The possible log types and their arguments are as follows:
core
The mirror is local and the mirror log is kept in core memory. This log type takes 1 - 3
arguments:
regionsize [[no]sync] [block_on_error]
disk
The mirror is local and the mirror log is kept on disk. This log type takes 2 - 4 arguments:
logdevice regionsize [[no]sync] [block_on_error]
clustered_core
The mirror is clustered and the mirror log is kept in core memory. This log type takes 2 - 4
arguments:
regionsize UUID [[no]sync] [block_on_error]
clustered_disk
The mirror is clustered and the mirror log is kept on disk. This log type takes 3 - 5 arguments:
logdevice regionsize UUID [[no]sync] [block_on_error]
LVM maintains a small log which it uses to keep track of which regions are in sync with the mirror
or mirrors. The regionsize argument specifies the size of these regions.
In a clustered environment, the UUID argument is a unique identifier associated with the mirror log
device so that the log state can be maintained throughout the cluster.
The optional [no]sync argument can be used to specify the mirror as "in-sync" or "out-of-sync".
The block_on_error argument is used to tell the mirror to respond to errors rather than ignoring
them.
#log_args
number of log arguments that will be specified in the mapping