SpecSFS2008 results NFS throughput vs. flash size – Chart of the Month

Scatter plot with SPECsfs2008 NFS throughput results against flash size, SSD, NFS thoughputThe above chart was sent out in our December newsletter and represents yet another attempt to understand how flash/SSD use is impacting storage system performance. This chart’s interesting twist is to try to categorize the use of flash in hybrid (disk-SSD) systems vs. flash-only/all flash storage systems.

First, we categorize SSD/Flash-only (blue diamonds on the chart) systems as any storage system that has as much or more flash storage capacity than SPECsfs2008 exported file system capacity. While not entirely true, there is one system that has ~99% of their exported capacity in flash, it is a reasonable approximation.  Any other system that has some flash identified in it’s configuration is considered a Hybrid SSD&Disks (red boxes on the chart) system.

Next, we plot the system’s NFS throughput on the vertical axis and the system’s flash capacity (in GB) on the horizontal axis. Then we charted a linear regression for each set of data.

What troubles me with this chart is that hybrid systems are getting much more NFS throughput performance out of their flash capacity than flash-only systems. One would think that flash-only systems would generate more throughput per flash GB than hybrid systems because of the slow access times from disk. But the data shows this is wrong?!

We understand that NFS throughput operations are mostly metadata file calls and not data transfers so one would think that the relatively short random IOPS would favor flash only systems. But that’s not what the data shows.

What the data seems to tell me is that judicious use of flash and disk storage in combination can be better than either alone or at least flash alone.  So maybe those short random IOPS should be served out of SSD and the relatively longer, more sequential like data access (which represents only 28% of the operations that constitute NFS throughput) should be served out of disk.  And as the metadata for file systems is relatively small in capacity, this can be supported with a small amount of SSD, leveraging that minimal flash capacity for the greater good (or more NFS throughput).

I would be remiss if I didn’t mention that there are relatively few (7) flash-only systems in the SPECsfs2008 benchmarks and the regression coefficient is very poor (R**2=~0.14), which means that this could change substantially with more flash-only submissions. However, it’s looking pretty flat from my perspective and it would take an awful lot of flash-only systems showing much higher NFS throughput per flash GB to make a difference in the regression equation

Nonetheless, I am beginning to see a pattern here in that SSD/Flash is good for some things and disk continues to be good for others. And smart storage system developers will do good to realize this fact.  Also, as a side note, I am beginning to see some rational why there aren’t more flash-only SPECsfs2008 results.

Comments?

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The complete SPECsfs2008 performance report went out in SCI’s December 2013 newsletter.  But a copy of the report will be posted on our dispatches page sometime this quarter (if all goes well).  However, you can get the latest storage performance analysis now and subscribe to future free newsletters by just using the signup form above right.

Even more performance information and ChampionCharts for NFS and CIFS/SMB storage systems are also available in SCI’s NAS Buying Guide, available for purchase from  website.

As always, we welcome any suggestions or comments on how to improve our SPECsfs2008  performance reports or any of our other storage performance analyses.

 

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