vault backup: 2025-04-11 16:02:40

1 files changed, 30 insertions, 0 deletions

diff --git a/Device mapper.md b/Device mapper.md
new file mode 100644
index 0000000..150338b
--- /dev/null
+++ b/Device mapper.md
@@ -0,0 +1,30 @@
+---
+tags:
+  - linux
+  - devices
+  - kernel
+---
+Device mapper is a kernel driver to map physical block devices to virtual ones; this means that for example we can have many physical devices be represented by a single virtual one (linear mapping).
+
+How does it work?
+What is its function in relation to multipath?
+
+Logical devices using device-mapper can be managed using `man 8 dmsetup`
+```
+[jasras@n04.compute.vps2-lej1 ~]$ sudo dmsetup info 3600a098038314d736724566a67346538
+Name:              3600a098038314d736724566a67346538
+State:             ACTIVE
+Read Ahead:        256
+Tables present:    LIVE
+Open count:        1
+Event number:      3
+Major, minor:      253, 12
+Number of targets: 1
+UUID: mpath-3600a098038314d736724566a67346538
+```
+
+If dmsetup cannot remove a device because a process still has it open, but lsof does not show any processes that open it, use `-f` which replaces the device with a fake that rejects all I/O.
+
+---
+[device-mapper](https://docs.redhat.com/en/documentation/red_hat_enterprise_linux/7/html/logical_volume_manager_administration/device_mapper#device_mapper)
+[dmsetup](https://docs.redhat.com/en/documentation/red_hat_enterprise_linux/7/html/logical_volume_manager_administration/dmsetup#dmsetup)
\ No newline at end of file