Why /dev/mapper

Get the major and nimor number of this device path. Match the major and minor numbers with system devices. Verify with lvdisplay in case of LVM. Notify me via e-mail if anyone answers my comment. A block device and offset is specified for each mirror leg, as indicated by the devs parameter.

The following example shows a mirror mapping target for a clustered mirror with a mirror log kept on disk. UUID of mirror log device to maintain log information throughout a cluster. The snapshot and snapshot-origin Mapping Targets. A device with a linear mapping containing the original mapping table of the source volume.

A device with a linear mapping used as the copy-on-write COW device for the source volume; for each write, the original data is saved in the COW device of each snapshot to keep its visible content unchanged until the COW device fills up.

A device with a snapshot mapping combining 1 and 2, which is the visible snapshot volume. The "original" volume which uses the device number used by the original source volume , whose table is replaced by a "snapshot-origin" mapping from device 1. A fixed naming scheme is used to create these devices, For example, you might use the following commands to create an LVM volume named base and a snapshot volume named snap based on that volume.

The format for the snapshot-origin target is as follows:. The snapshot-origin will normally have one or more snapshots based on it. Reads will be mapped directly to the backing device. For each write, the original data will be saved in the COW device of each snapshot to keep its visible content unchanged until the COW device fills up. The format for the snapshot target is as follows:. 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.

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 The following example shows a snapshot target with an origin device of and a COW device of This snapshot device is persistent across reboots and the chunk size for the data stored on the COW device is 16 sectors.

The error Mapping Target. 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 zero Mapping Target. A read operation to this mapping returns blocks of zeros. Data written to this mapping is discarded, but the write succeeds. The zero mapping target takes no additional parameters besides the start and length parameters.

The following example shows a zero target for a 16Tb Device. The multipath Mapping Target. The multipath mapping target supports the mapping of a multipathed device. The format for the multipath target is as follows:. There is one set of pathgroupargs parameters for each path group.

The number of multipath features, followed by those features. If this parameter is zero, then there is no feature parameter and the next device mapping parameter is handlerargs. Improve this question. Gilles 'SO- stop being evil' k gold badges silver badges bronze badges. Tosh Tosh 1 1 gold badge 6 6 silver badges 11 11 bronze badges.

Add a comment. Active Oldest Votes. Improve this answer. Gilles 'SO- stop being evil' Gilles 'SO- stop being evil' k gold badges silver badges bronze badges. But these ones look like they are.

They follow the naming convention that LVM uses. Some unix systems e. Linux don't care. Tosh You can run lsblk to view the storage tree, or vgs and lvs to list volume groups and logical volumes. Ahm, without LVM output there is hardly a chance to understand what options you have and what might be a good solution. Check vgdisplay and lvdisplay. And please post ouputs properly quoted, otherwise they are hardly readable after posting. Are these two disks separate physical disks?

They are not separate disks actually. Then, you can follow instructions from Jorge's answer below. Add a comment. Active Oldest Votes. What if there's no space in the VG? Improve this answer. Jorge Valentini Jorge Valentini 3 3 silver badges 9 9 bronze badges. Thanks bro, one day i spent to search for this solution. Efficient, and Useful, perfect. Glad it helped. This doesn't have enough information in it to be useful — A X.