Thursday, September 5, 2013

Size Matters!

Hi Friends,

I'm here today to answer the age old question, does size matter?  Without a doubt, size matters!  When it comes to sizing your VDI storage.  :-)

Okay, now get your mind out of the gutter and let's talk about block size!  Yeah I know, the gutter is probably more fun, but unless I want to start a trashy romance blog, let's stick to technical stuff.

So IOPS, what the heck are IOPS?  IOPS are input and output operations per second.  Okay....  So what's are IOPS?  Basically it's a performance measurement commonly used, particularly for hard drives.  And since storage is made up of hard drives, I hear the term a lot!  So much so that it's become one of the leading metrics people use to size their environments when they're getting ready implement a new storage system for VDI.

Unfortunately IOPS are only part of the story.  Take my friend here. He's strong, and confident he can lift 10 IOPS of work.  And if IOPS were the only performance metric we needed to worry about, my friend here could lift 10 IOPS all day!

Ah, but IOPS are not the only thing we need to worry about friends.  What about Reads vs. Writes?

How about Sequential vs. Random work load?  And the Hypervisor?

And what about Block Size??

As my friend here has demonstrated, all of these performance metrics can squash your storage performance if you haven't sized for them.  Due to the random nature of desktops, block size can be 4KB one moment and 64KB another!  Although it might not sound like much, 10 IOPS of 4KB work is a lot less the 10 IOPS of 64KB work.

The beauty of Nimble Storage is the CASL OS and it's extreme flexibility.  Unlike my friend here who as a lot on his mind now, CASL is optimized to handle the randomness and extremes of a VDI workload.

So remember size DOES matter! If you start to get yourself in a position where IOPS are becoming the predominant topic of a sizing discussion, remember my flat friend and get that conversation on track!

Until Next Time


  1. Now, I want a graphic of your friend juggling all the different weights.

    That's CASL, BABY!

  2. how does VMware handle different block sizes on vmfs? You are still advocating using guest connected luns and volumes for virtual workloads, right? what about supporting with a 100% virtual environment with data on vdisks versus LUNs and volumes? does block size matter then (does it need to?)

    nice stick figures :)

  3. Hi, Thanks for the comment! There's a couple of things here. The block size I was referring to is how the applications running on Windows 7 write to the virtual disk on the storage array. That can vary with large blocks one moment and small blocks another. This is just the nature of running apps on an OS and will always happen.

    What I think you're referring to is different ways you can attach storage to that virtual machine and how block size can change it's performance characteristics. It's true that attaching LUNs in a variety of ways can change the block size characteristics. The most common I'm thinking of is introducing misalignment if your LUN is not aligned with whatever block size your storage array is presenting it's storage out at. (4K, 8K, etc.) The cool thing about Nimble Storage is you can change that block size when you're creating your volume.

    Let me know if I answered your question or just confused things. :-)

    Best Regards,