Hardware RAID controllers are complex devices: essentially, it’s a computer inside a computer. It has it’s own processor (or may be processors), it usually has it’s own RAM, and, most important, it runs its own software, which is usually a fairly complex operating system that manages physical discs, hides all the RAID magic behind the curtains and allows the host operating system to see only few logical discs.

Unfortunately, most of the RAID controllers are proprietary. It’s a well-known fact that physical discs used on controller A are incompatible with some other controller B (even worse, they can be incompatible between various revisions of firmware of controller A). RAID’s firmware hides all the intricate management of discs from the system administrator. Administrator can control RAID using either:

Einarc project tries to solve such problem: provide a unified, solid interface to manage all possible storage devices.

Einarc unifies various RAIDs and storage devices, providing a simple object interface for end-user. Inside, it works as a proxy, translating commands from that object interface to RAID-specific commands for it’s proprietary CLI, and back, it translates response from proprietary CLI into unified answer.

Figure 1. Einarc architecture diagram

Support for various RAIDs is implemented as classes. Each class has to implement a couple of methods that would translate requests.

Currently, there are following modules available:

This is not a complete list. To check if your adapter is supported, just run ./configure or einarc-install without options to select all available modules. There’s a good chance that your adapter would be supported too.

Currently, Einarc is a sub-project of Inquisitor hardware testing framework and can be downloaded either bundled with Inquisitor itself or from its own mini-homepage. Alternatively, your favourite distributed may provide you with pre-built package.

Simplest way to use Einarc is to use command-line interface. Einarc can be invoked using:

einarc [options] <object> <method> <parameters>

Options:

Refer to object interface description for particular object.

Note that command-line interface is always ready to provide a hint. For example, one can forget almost everything and start with just calling "einarc". Consider this session:

$ einarc
Adapter type not specified: use --list to list all adapters and choose one
$ einarc --list
areca   1       ARC-1160        PCI
$ einarc -h -t areca
Object not specified; available objects: logical, log, adapter, task, physical

Let’s start with showing all logical drives. We don’t know what method we should choose, but Einarc will give a hint:

$ einarc -h -t areca logical
Command not specified; available commands: list, add, delete, clear, get, set
$ einarc -h -t areca logical list
#  RAID level   Physical drives                 Capacity     Device  State
1  5            0:1,0:2,0:4,0:5,0:8            762939.45 MB          normal
2  1+0          0:6,0:7                        190734.86 MB          normal
3  5            0:9,0:10,0:11,0:12,0:13       1907348.63 MB          normal
4  1+0          0:15,0:16                      476837.16 MB          normal

More complex example: let’s check if a physical drive is hotspare drive or not. Such simple boolean flag is available as a property of physical object, and Einarc will give a hint on how to get it and when to add a reference to particular physical disc ID:

$ einarc -h -t areca physical
Command not specified; available commands: list, get, set
$ einarc -h -t areca physical get
Object identifier not specified
$ einarc -h -t areca physical get 0:1
Property not specified; available properties: hotspare
$ einarc -h -t areca physical get 0:1 hotspare
0

Getting a property of adapter is in fact even simpler: there shouldn’t be any IDs. Here we’ll get a list of all RAID levels a particular adapter supports:

$ einarc -h -t areca adapter
Command not specified; available commands: info, restart, get, set
$ einarc -h -t areca adapter get
Property not specified; available properties: raidlevels
$ einarc -h -t areca adapter get raidlevels
0
1
1E
10
3
5
6

Einarc’s libraries can be called directly with almost the same object terms as from the command-line interface.

Einarc is written in Ruby and thus can be used easily from this script language. Using Einarc API in your program takes a few simple steps:

require 'raid/baseraid'

RAID::BaseRaid.query_adapters

[{:driver=>"areca", :version=>"PCI", :num=>1, :model=>"ARC-1160"}]

a = RAID::Areca.new

Einarc exposes a relatively simple and straight-forward object model for an end-user.

Figure 2. Einarc objects

Every computer (host) may have one or more adapters (object adapter). Adapters provide RAID services as logical discs (object logical) that are usually seen in OS as individual devnodes. Logical discs may include one or more physical discs (object physical). Physical discs are usually hidden from the OS and are accessible only through proprietary CLI. Adapters also may keep some history of what events happened in the past and what objects were involved (object log). Finally, adapters being little computers with their own operating system and multi-tasking may perform separate background tasks, such as building/rebuilding or checking of the array (object task).

Each of these objects have a couple of methods described below. Some of these objects have named properties that can be read using get and written using set. Some of the properties are read-only (only get would work), some are write-only (only set would work).