Installation guide

The error Mapping Target
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start
starting block in virtual device
length
length of this segment
origin
base volume of snapshot
COW-device
Device on which changed chunks of data are stored
P|N
P (Persistent) or N (Not persistent); indicates whether snapshot will survive after reboot. For
transient snapshots (N) less metadata must be saved on disk; they can be kept in memory by the
kernel.
chunksize
Size in sectors of changed chunks of data that will be stored on the COW device
The following example shows a snapshot-origin target with an origin device of 254:11.
0 2097152 snapshot-origin 254:11
The following example shows a snapshot target with an origin device of 254:11 and a COW device
of 254:12. This snapshot device is persistent across reboots and the chunk size for the data stored on
the COW device is 16 sectors.
0 2097152 snapshot 254:11 254:12 P 16
A.1.5. The error Mapping Target
With an error mapping target, any I/O operation to the mapped sector fails.
An error mapping target can be used for testing. To test how a device behaves in failure, you can
create a device mapping with a bad sector in the middle of a device, or you can swap out the leg of a
mirror and replace the leg with an error target.
An error target can be used in place of a failing device, as a way of avoiding timeouts and retries on
the actual device. It can serve as an intermediate target while you rearrange LVM metadata during
failures.
The error mapping target takes no additional parameters besides the start and length
parameters.
The following example shows an error target.
0 65536 error
A.1.6. The zero Mapping Target
The zero mapping target is a block device equivalent of /dev/zero. A read operation to this
mapping returns blocks of zeros. Data written to this mapping is discarded, but the write succeeds.