Linux Internals

Device-mapper is a very important component of Linux 2.6 kernel. It is used for many critical storage related applications, such as LVM2, Linux native multipath tool device-mapper-multipath, device-mapper software RAID, etc. A solid understanding of device-mapper helps system administrators to investigate various kinds of issues with these applications. In the Linux kernel, the device-mapper is a generic framework to map one block device into another. It is not just for LVM2. By using device-mapper, the kernel provides general services to dm-multipath, LVM2 and EVMS, device-mapper software RAIDs, dm-crypt disk encryption and offers additional features such as file system snapshots. In device-mapper architecture there are three important concepts to be familiarized 1. Mapped Device 2. Mapping Table 3. Target Device Mapped Device Mapped device is a logical device provided by device-mapper driver. It provides an interface to operate on. The logical volumes in LVM2 and pse...