SPC and Storage Benchmarking Games

July 6, 2009 – 11:47 am

Storage I/O trends

There is a post over in one of the LinkedIn Discussion forums about storage performance council (SPC) benchmarks being miss-leading that I just did a short response post to. Here’s the full post as LinkedIn has a short post response limit.

While the SPC is far from perfect, it is at least for block, arguably better than doing nothing.

For the most part, SPC has become a de facto standard for at least block storage benchmarks independent of using IOmeter or other tools or vendor specific simulations, similar how MSFT ESRP is for exchange, TPC for database, SPEC for NFS and so forth. In fact, SPC even recently rather quietly rolled out a new set of what could be considered the basis for Green storage benchmarks. I would argue that SPC results in themselves are not misleading, particularly if you take the time to look at both the executive and full disclosures and look beyond the summary.

Some vendors have taken advantage of the SPC results playing games with discounting on prices (something that’s allowed under SPC rules) to show and make apples to oranges comparisons on cost per IOP or other ploys. This proactive is nothing new to the IT industry or other industries for that matter, hence benchmark games.

Where the misleading SPC issue can come into play is for those who simply look at what a vendor is claiming and not looking at the rest of the story, or taking the time to look at the results and making apples to apples, instead of believing the apples to oranges comparison. After all, the results are there for a reason. That reason is for those really interested to dig in and sift through the material, granted not everyone wants to do that.

For example, some vendors can show a highly discounted list price to get a better IOP per cost on an apple to oranges basis, however, when processes are normalized, the results can be quite different. However here’s the real gem for those who dig into the SPC results, including looking at the configurations and that is that latency under workload is also reported.

The reason that latency is a gem is that generally speaking, latency does not lie.

What this means is that if vendor A doubles the amount of cache, doubles the number of controllers, doubles the number of disk drives, plays games with actual storage utilization (ASU), utilizes fast interfaces from 10 GbE  iSCSI to 8Gb FC or FCoE or SAS to get a better cost per IOP number with discounting, look at the latency numbers. There have been some recent examples of this where vendor A has a better cost per IOP while achieving a higher number of IOPS at a lower cost compared to vendor B, which is what is typically reported in a press release or news story. (See a blog entry that also points to a CMG presentation discussion around this topic here.

Then go and look at the two results, vendor B may be at list price while vendor A is severely discounted which is not a bad thing, as that is then the starting list price as to which customers should start negotiations. However to be fair, normalize the pricing for fun, look at how much more equipment vendor A may need while having to discount to get the price to offset the increased amount of hardware, then look at latency.

In some of the recent record reported results, the latency results are actually better for a vendor B than for a vendor A and why does latency matter? Beyond showing what a controller can actually do in terms of levering  the number of disks, cache, interface ports and so forth, the big kicker is for those talking about SSD (RAM or FLASH) in that SSD generally is about latency. To fully effectively utilize SSD which is a low latency device, you would want a controller that can do a decent job at handling IOPS; however you also need a controller that can do a decent job of handling IOPS with low latency under heavy workload conditions.

Thus the SPC again while far from perfect, at least for a thumb nail sketch and comparison is not necessarily misleading, more often than not it’s how the results are utilized that is misleading. Now in the quest for the SPC administrators to try and gain more members and broader industry participation and thus secure their own future, is the SPC organization or administration opening itself up to being used more and more as a marketing tool in ways that potentially compromise all the credibility (I know, some will dispute the validity of SPC, however that’s reserved for a different discussion ;) )?

There is a bit of Déjà here for those involved with RAID and storage who recall how the RAID Advisory Board (RAB) in its quest to gain broader industry adoption and support succumbed to marketing pressures and use or what some would describe as miss-use and is now a member of the “Where are they now” club!

Don’t get me wrong here; I like the SPC tests/results/format, there is a lot of good information in the SPC. The various vendor folks who work very hard behind the scenes to make the SPC actually work and continue to evolve it also all deserve a great big kudos, an “atta boy” or “atta girl” for the fine work that have been doing, work that I hope does not become lost in the quest to gain market adoption for the SPC.

Ok, so then this should all then beg the question of what is the best benchmark. Simple, the one that most closely resembles your actual applications, workload, conditions, configuration and environment.

Ok, nuff said.

Cheers gs

Greg Schulz – Author Cloud and Virtual Data Storage Networking (CRC Press), The Green and Virtual Data Center (CRC Press) and Resilient Storage Networks (Elsevier)
twitter @storageio

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