Volume Management: Virtualizing Host Storage

I’ve been feverishly preparing for my upcoming TechTarget seminar series focused on storage virtualization, so I thought it might be interesting to post a few topics from the talk here on the blog.  If you’ll be in Washington DC on March 4, or Durham NC on March 6 and are interested in the world of storage and server virtualization, I’d love for you to register and attend this free seminar!

I’m kicking off with one of my favorite topics, logical volume management on servers. This is the longest-standing and most-successful face of storage virtualization, and the one I was first exposed to. Put simply, volume managers abstract block storage (LUNs, disks, partitions, what have you) into virtual “volumes” for use by the server. They look the same to the OS, and still need a filesystem, but are much more flexible, as we’ll see.

Volume managers are very common today – all modern OSes (except for that one from Apple!) have volume managers built in. Windows has the Logical Disk Manager, which I’m told was co-engineered (or something) with Veritas way back when and which I’ve covered in my Storage Magazine columns. Linux has an implementation of LVM, which I wrote something about way back when, and which has now not been supplanted by EVMS as had once been supposed. AIX it’s own twist on the original LVM, as does HP-UX. Solaris has the variously-named Solstice DiskSuite/Volume Manager which has evolved substantially in the 15 or so years I’ve been using it. And everyone has Symantec’s Veritas Volume Manager/Foundation Suite, which we in “the biz” view with considerable admiration and some skepticism, as is the case with all good front runners!

Folks mostly use volume managers for flexibility. It’s really quite amazing what you can do when your servers run them, enough that you often wonder how you got along without them!

• You can resize volumes (aka file systems or drives) on the fly (if your file system supports this as most modern ones do)
• You can protect data with RAID, even if your storage doesn’t support it (think bare disk drives)
• You can add storage capacity on the fly by concatenating new to old or (maybe) expanding existing stripes and RAID sets
• You can mirror volumes, create snapshots, and even replicate data to remote locations (this functionality varies by product, of course)
• One of the most powerful things (to me) was the ability to migrate live volumes from one storage device to another when making infrastructure changes

In short, volume management = server-based storage virtualization! So even if you were skeptical about the claims about storage virtualization, you might already be using it! Amazingly, a good volume manager can do anything a storage virtualization appliance or enterprise storage array can do. In fact, some virtualization appliances have more than a little volume management source code in them…

And the only cost for all this great stuff is the impact on your server’s CPU, memory, bus, access control, etc… 😉

The chart below compares the major volume managers, and includes a little easter egg at the bottom… But we’ll cover that on another day.