Synnefo » snf-ganeti » ganeti-local

Storage units modelling

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Currently, Ganeti has a good model of the block devices for instances

(e.g. LVM logical volumes, files, DRBD devices, etc.) but none of the

storage pools that are providing the space for these front-end

devices. For example, there are hardcoded inter-node RPC calls for

volume group listing, file storage creation/deletion, etc.

The storage units framework will implement a generic handling for all

kinds of storage backends:

- LVM physical volumes

- LVM volume groups

- File-based storage directories

- any other future storage method

There will be a generic list of methods that each storage unit type

will provide, like:

- list of storage units of this type

- check status of the storage unit

Additionally, there will be specific methods for each method, for example:

- enable/disable allocations on a specific PV

- file storage directory creation/deletion

- VG consistency fixing

This will allow a much better modeling and unification of the various

RPC calls related to backend storage pool in the future. Ganeti 2.1 is

intended to add the basics of the framework, and not necessarilly move

all the curent VG/FileBased operations to it.

Note that while we model both LVM PVs and LVM VGs, the framework will

**not** model any relationship between the different types. In other

words, we don't model neither inheritances nor stacking, since this is

too complex for our needs. While a ``vgreduce`` operation on a LVM VG

could actually remove a PV from it, this will not be handled at the

framework level, but at individual operation level. The goal is that

this is a lightweight framework, for abstracting the different storage

operation, and not for modelling the storage hierarchy.