Friday, June 21, 2013

Let’s Talk About CASL - Why Hybrid Storage

Hi Friends,

Today I’d like to talk to you about CASL.

Nope, not CASTLE, CASL.   

I’m referring to Nimble’s Cache Accelerated Sequential Layout.  If storage was a burger, CASL would be the secret sauce!  It looks like Thousand Island dressing, but man it’s NOT Thousand Island dressing!

In today’s market everyone is SSD happy.  I’m waiting to hear SSD’s cured world hunger and war!  Don’t get me wrong SSD’s are cool, but I don’t think they are the panacea everyone has labeled them to be.  If I were an SSD I’d be STRESSED with all the pressure people put on me!  They’re expensive, they have a finite life, and oh did I mention they’re expensive?

If you have more money to spend then you know what to do with, well then I guess you should just buy what you want!   And if you have that much money, you should retire and go have fun, what are you doing working?!  Anyway, I digress…  If you’re like the rest of us, on a budget, and you’re looking for the best solution for the money, how about a hybrid option?

Nimble Storage has done something very clever; they’ve taken spinning media and complemented it with SSD’s giving a killer synergistic effect.  It’s really quite cool.  Nimble coalesces random or sequential inbound data blocks and writes them sequentially to the spinning disks to optimize write time while compressing the data at the same time to save space.  Nimble doesn’t over write an existing changed block, which speeds up write time since that block is marked for cleanup at a later time.  While the coalesced sequential writes are happening a cleanup or sweep is running in other parts of the disk to cleanup those old blocks.

Think of it as a conveyor belt moving around.  As old blocks are cleaned up, disk space moves back to the front of the line waiting for more new blocks.  In the middle we have stored data that can be at rest, but at any moment can be retrieved for a user request.

So what about reads?  When they’re accessed from disk, they’re put into cache so the next time a request for those blocks is called upon they’re don’t have to come from spinning media.  Giving smoking fast response time.

With Nimble you get the best of both worlds!

Until Next Time!


  1. I love In&Out Grill cheese.

    >> If storage was a burger, CASL would be the secret sauce! It looks like Thousand Island dressing, but man it’s NOT Thousand Island dressing!

    How is data written on cache?

  2. There food is good there! :-) Ever had the Animal Fries? OH, so good!!

    CASL writes to cache a couple of ways. The first way is random writes get written to cache and eventually to disk. The second is reads that aren't available in cache go to disk and those are called a cache miss. CASL will go down to the disk layer, retrieve the data and put it into cache for faster reads the next time the data is read.

    I hope this helps!