In his 2000 OLS talk, Ken Preslan talks about some older software like "pool" and "memexp". I want to make sure I understand how things have changed since 2000. Are the following paragraphs correct? Pool is software that the GFS folks created before LVM was ready. LVM does volume management today, and pool is obsolete. One of the features of pool that he mentions is also in LVM: identifying physical block devices by their contents instead of their location. The example he gives is of a SCSI drive in a fiber channel network, where adding a drive in one room can change the LUN of a drive in another room. Pool allowed tracking of drives regardless of their location. LVM does the same thing. The memexp locking module that was new at the time of the 2000 OLS talk was designed to use RAM exported by fancy storage hardware for coordinating locking. A single node could stand in, though, taking the place of the fancy RAM-exporting storage hardware. Today, most GFS installations use DLM instead. Preslan mentions that after acquiring a lock, a node must "heartbeat the drive" because the locking state is on the storage hardware. How is that done these days? Does a lock owner heartbeat the lock master or does cluster management take care of this issue? -- Ed L Cashin <ecashin@xxxxxxxxxx>
