Logical Volumes and the VSX

Logical volumes are simple to create and manage using the Coraid EtherDrive VSX. For the uninitiated, logical volumes allow for flexibility in how you manage your storage, even over multiple SRX appliances.

Creating a logical volume begins with making a pool. Let’s call the one I’m making today “sales.” This pool is nothing more than a group of physical volumes that your VSX will chop up and rearrange to form logical volumes.

I typically create my pools by grouping whatever media on the back end that best serves the project at hand. So let’s say I have a handful of speedy SSDs in one of my SRXs that would be perfect for my new sales pool. To make these drives visible to the VSX, I’d create a RAID5 and online it just like any other SRX LUN. That’s all it takes to make a physical volume for your pool.

Before I jump into creating my first logical volume from the sales pool, I need to add this new physical volume to the pool using a simple command (mkpv). Once I do, the VSX will create an inventory of 4MB extents. These are small chunks of physical volumes that become the raw materials that logical volumes are made of and provide the flexibility our storage needs.

Now I’m ready to create my first logical volume from the sales pool. The beauty of logical volumes is that because they are made of independent 4MB extents, they can be any size needed. They could even be spread over several physical volumes or even multiple SRX appliances. This flexibility is great because if I need more room in a pool, I can just add more physical volumes to that pool. It doesn’t matter where the physical volumes are housed.

Provisioning, and deciding exactly how to do so, is another perk of logical volumes. Do we want to allocate all the storage up front to make sure you have room for everything? Or, do we want to “thin provision” the volume?

Thin provisioning merely means only allocating extents when they’re needed. This feature is particularly handy when you have a project leader insisting that they need 10TB of storage, but you know better. Rather than getting bogged down in a debate, all you have to do is thin provision the 10TB and just watch it and see what happens. As they use space, you can always add more PVs to the pool, creating more raw materials for the VSX to work with.

So to recap, all you have to do to use logical volumes with the SRX is…

1. Create a pool.
2. Add physical volumes to the pool.
3. Create logical volumes from the pool.
4. Put the logical volume online as a VSX LUN.

That’s it. Those four little steps make managing storage fast and flexible, essential for your ever-changing storage needs.