The DAS disruption series has been driven by a belief that expanding memory sizes change the fundamental behavior of storage systems. What I’ve argued is that expanding memory sizes put an increasing premium on the ability to do efficient write operations and an increasingly low premium on the ability to do read operations. And I have argued that the future belongs to the Better Than Fibre Channel Array vendors who have optimized their systems for write performance.
It’s always gratifying when your company releases technology that buttresses your point :-)
The tier to shed isn’t FC, it’s SSD!
And just to be clear, the point of this post isn’t to argue FC is dead. because that’s too easy. The point of this post is to argue that Flash as a stable storage medium is dead.
The PAM II is NetApp’s Flash memory card. Unlike SSD’s that can only accelerate data that is stored on the SSD, the PAM II allows NetApp to cost effectively extend the buffer cache for all data in a system. Because the PAM II is a buffer no expensive complex data distribution system like FAST is required.
The PAM II allows a customer to add 256 512 GB of Flash memory per card to the system buffer cache, reducing the total IOPS that the disk subsystem has to perform across the entire dataset stored in the system. The PAM II and the surrounding software architecture allows NetApp to leverage flash for hot data, while leaving disk to store cold automatically.
There are lots of ways to make the point, but this particular set of graphs makes it quite eloquently.
Using hardware that has worse latency than FC, the latency of the storage system was about the same with fewer spindles for all of the data.
What’s going on is that the although the total number of write operations has stayed the same, the total number of read operations from disk have gone down. Because the read operations are being served from high speed flash, the total latency actually delivered from the storage device is better than a system that uses FC drives.
For those who followed our previous announcements on the PAMvI, this is no surprise.
And now for more mission critical workloads…
What should be more interesting to folks is that we’re able to achieve similar results for OLTP workloads (aka mission critical).
In a recently produced white paper Using the Performance Accelerator Module II in Online Transaction Processing, NetApp demonstrates that a PAMvII is equivalent to doubling the number of disks:
And at the same time improving the system response time:
I’ve said it before, and I’ll say it again, Flash is a part of the volatile memory hierarchy, not the storage hierarchy. Flash is most efficiently and effectively used as a cache not a solid state device.





