XIV Gen3 spot the differences part two: Open the door

Last week I talked about the differences between the XIV Generation 2 and XIV Gen3 by just looking at the rack.   This week we open the front door to see if we can spot any more differences…

First up you notice that it looks almost exactly the same…..   but appearances can be deceiving.

So what actually is different?  From the front there are three obvious visible differences, two of which are not that interesting….

1. The XIV Generation 2 has a storage grid that uses two 48 port Gigabit Ethernet network switches for interconnection between the modules (these are only visible from around the back of the rack).  However these switches get redundant power via an RPS-600 Redundant Power Supply (RPS) which sits at the front of the rack (directly above module 6).
   The XIV Gen3 on the other hand uses two 36 port Infinband switches that have redundant power supplies built in.  So the Gen3 does not need the RPS.  Thus in the XIV Gen3 it is no longer there.  But its spot has not remained empty….
2. The XIV Generation2 has a special server called a Maintenance Module located at the rear of the rack.  You may notice the USB modem plugged into it.  The XIV Gen3 uses an IBM System x3250 M3 mounted at the front of the rack.   This server is used for maintenance, upgrades and remote access (if necessary, via modem).  You can spot it here directly below the nameplate where the RPS used to be:
   
3. If you look closely at the disks in a Gen3 you will notice they are marked as SAS drives, not SATA.  This gives us a performance boost even though the rotation speed remains the same.If you want to see this closeup yourself, check out this Kaon 3D model of the XIV Gen3.

This got me wondering why SAS drives that have the same rotational speed and seek time as SATA drives, could perform better.   The main two reasons are that SAS is full duplex and that SAS supports tagged command queuing.  There is a great article regarding the differences here that references SPC testing that Seagate performed.    A quote from the article:

SAS drives offer a significant improvement in performance over SATA drives in both throughput and IOPs primarily due to their full duplex, bi-directional I/O capabilities. Published Storage Performance Council (SPC) benchmark results demonstrate this feature with up to 64 percent improvement in the SPC-2 benchmark (based on multiple workload testing).

Wikipedia also talks about the differences here.

So is that it for differences between XIV Generation 2 and Gen3?   Well visibly from the front… yes it is.  The big changes are around the back and inside the modules, which I will cover in a future blog post.

In the meantime, check out my new Visios for XIV.  I have added three new stencils (which I am still working on).   Check them out and let me know what you think.   You will find them here.   If and when I update them, you will get a notification so you can keep up to date.