Friday August 05, 2005

Fun with state database replicas (Part 1) As I mentioned in my last entry, information about SVM metadevices is stored in state database replicas(mddbs). The data structures used in state database replicas are defined in: usr/src/uts/common/sys/lvm/md_mddb.h
The following is a drawing of diskset mddb:

1) The Master Block

The master block contains two important pieces of information, a unique device identifier(devid) and the offset for the locator block.* The devid is used by SVM to track the drives that are in a set--so that SVM can handle changes in their physical location. The master block contains the mapping from a logical block 0 to the physical offset for the mddb's locator block. If there are two mddbs on the same slice, they will each have a different master block--the location of the first metadb will be at 0 and the second at 8192. The master block and locator block are the only two parts of an mddb who's location always remains constant. All drives in a diskset either contain a mddb or a dummy master block. The dummy master block is primarily used to store the devid for the drive.

* In replicated disksets, the master block does not have a devid for the drive it is on, rather it contains a copy of the devid for the original drive.

OpenSolaris
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