Storage Groups

Alteeve Wiki :: How To :: Storage Groups

In an Anvil! cluster, a "storage group" is a logical group of LVM Volume Groups. When a server is created, the selected storage group tells the cluster where to pull the physical storage from to create the server's virtual hard drive. Most Anvil! nodes have only one VG per subnode and they are generally the same size. As such, the Anvil! is able to automatically link them into a storage group automatically.

Multi-VG Example

Consider a more complex storage configuration, however.

Lets use the example of subnodes with two RAID arrays; The first is made of high speed flash drives, and the second made up of lower speed bulk storage drives. In this case, there will be two storage devices on the nodes;

Block Device	Purpose
/dev/sda	Bulk storage, slow drives. The subnode's OS is installed on this array.
/dev/sdb	Smaller but faster drives, reserved for specific guest servers with high speed storage requirements.

During the OS installation stage, /dev/sda3 is used as the LVM physical volume, or "PV".

Node: an-anvil-01

Subnode	Physical Volume	Volume Group	Type
an-a01n01	/dev/sda3	an-a01n01_vg0	Bulk storage, slow drives. The subnode's OS is installed on this array.
an-a01n02	/dev/sda3	an-a01n02_vg0

After the OS is installed, the /dev/sdb1 partition is used as the PV and used to back a second VG;

Node: an-anvil-01

Subnode	Physical Volume	Volume Group	Type
an-a01n01	/dev/sdb1	an-a01n01_vg1	Smaller but faster drives, reserved for specific guest servers with high speed storage requirements.
an-a01n02	/dev/sdb1	an-a01n02_vg1

Virtual Hard Drives

When a server is created, a virtual hard drive is created to back the storage of that server. Behind the scenes though, an LVM logical volume is created on each subnode, and those are used to back the replicates storage device.

Consider an example server we'll call 'srv01-database'. This looks like this

Server: srv01-database on an-a01n01.

Subnode	Volume Group	Logical Volume	Replicated Volume
an-a01n01	an-a01n01_vg0	/dev/an-a01n01_vg0/srv01-database_0	/dev/drbd/by-res/srv01-database/0
an-a01n02	an-a01n02_vg0	/dev/an-a01n02_vg0/srv01-database_0

At this point, you might be asking yourself; "How did the new server decide to use the bulk storage array? What if I wanted to use the high speed storage?".

This is where Storage Groups come in to play!

Storage Groups; Linking VGs

 

Any questions, feedback, advice, complaints or meanderings are welcome.
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