Not a lot of Storage Performance Council (SPC) benchmark submissions this past quarter just a new SPC-1/E from HP StorageWorks on their 6400 EVA with SSDs and a new SPC-1 run for Oracle Sun StorageTek 6780. Recall that SPC-1/E executes all the same tests as SPC-1 but adds more testing with power monitoring equipment attached to measure power consumption at a number of performance levels.
With this chart we take another look at the storage energy consumption (see my previous discussion on SSD vs. drive energy use). As shown above we graph the IOPS/watt for three different performance environments: Nominal, Medium, and High as defined by SPC. These are contrived storage usage workloads to measure the varibility in power consumed by a subsystem. SPC defines the workloads as follows:
Nominal usage is 16 hours of idle time and 8 hours of moderate activity
Medium usage is 6 hours of idle time, 14 hours of moderate activity, and 4 hours of heavy activity
High usage is 0 hours of idle time, 6 hours of moderate activity and 18 hours of heavy activity
As for activity, SPC defines moderate activity at 50% of the subsystem’s maximum SPC-1 reported performance and heavy activity is at 80% of its maximum performance.
With that behind us, now on to the chart. The HP 6400 EVA had 8-73GB SSD drives for storage while the two Xiotech submissions had 146GB/15Krpm and 600GB/15Krpm drives with no flash. As expected the HP SSD subsystem delivered considerably more IOPS/watt at the high usage workload – ~2X the Xiotech with 600GB drives and ~2.3X the Xiotech with 146GB drives. The multipliers were slightly less for moderate usage but still substantial nonetheless.
SSD nominal usage power consumption
However, the nominal usage bears some explanation. Here both Xiotech subsystems beat out the HP EVA SSD subsystem at nominal usage with the 600GB drive Xiotech box supporting ~1.3X the IOPS/watt of the HP SSD system. How can this be? SSD idle power consumption is the culprit.
The HP EVA SSD subsystem consumed ~463.1W at idle while the Xiotech 600GB only consumed ~23.5W and the Xiotech 146GM drive subsystem consumed ~23.4w. I would guess that the drives and perhaps the Xiotech subsystem have considerable power savings algorithms that shed power when idle. For whatever reason the SSDs and HP EVA don’t seem to have anything like this. So nominal usage with 16Hrs of idle time penalizes the HP EVA SSD system resulting in the poors IOPS/watt for nominal usage shown above..
Rays reading: SSDs are not meant to be idled alot and disk drives, especially the ones that Xiotech are using have very sophisticated power management that maybe SSDs and/or HP should take a look at adopting.
The full SPC performance report will go up on SCI’s website next month in our dispatches directory. However, if you are interested in receiving this sooner, just subscribe by email to our free newsletter and we will send you the current issue with download instructions for this and other reports.
As always, we welcome any suggestions on how to improve our analysis of SPC performance information so please comment here or drop us a line.
Well maybe that overstates the case but there is no denying that both fatter (higher capacity) drives and flash memory (used as cache or in SSDs) saves energy in today’s data center. The interesting thing is that the trend to higher capacity drives has been going on for decades now (see chart) but only within the last few years has been given any credit for energy reduction. In contrast, flash in SSDs and cache is a relative newcomer but saves energy nonetheless.
I almost can’t recall when disk drives weren’t doubling in capacity every 18 to 24 months. The above chart only shows PC drives capacities over time but enterprise drives have followed a similar curve. The coming hard drive capacity wall may slow things down in the future but just last week IBM announced they were moving from a 300GB to a 600GB 15Krpm enterprise class disk drive in their DS8700 subsystem. While doubling capacity may not quite halve energy use, it’s still significant. Such energy reductions are even more dramatic with slower, higher density disks. These SATA disks are moving from 1TB to 2TB later this year and should cut energy use considerably.
Similarly, NAND flash density used in SSDs is increasing capacity at almost a faster rate than disk storage. ASIC feature size continues to shrink and as such, more and more flash storage is packed onto the same die size. Improvements like these are doubling the capacity of SSDs and flash memory. While SSD power reduction due to density improvements may not be as significant as disk, we hope to see a flattening out of power use per NAND cell over time. This flattening out of power use is now happening with processing chips and we see little reason why similar techniques couldn’t apply to NAND.
But the story with flash/SSDs is a bit more complicated:
SSDs don’t consume as much energy as a standard disk drive at the same capacity, so a 146GB enterprise class SSD should consume much less energy than a 146GB enterprise class disk drive.
SSDs don’t exhibit the significant energy spike that hard disk drives encounter when driven at higher IOPs and was discussed in SSDs vs. Drives energy use.
SSDs can often replace many more disk spindles than pure capacity equivalence would dictate. Some data centers use more disks than necessary to spread workload performance over more spindles wasting storage, power and cooling. Moving this data to SSDs or adding flash cache to a subsystem, spindle counts can be reduced dramatically and as such, slash energy use for storage.
All this says that using SSDs or flash in place of disk drives reduces data center power requirements. So if you’re interested in saving energy and thus, helping to save the planet, buy fat(ter) disks and flash for your data storage needs.
Brought to you on behalf of Planet Earth in honor of Earth Day.
Recently, the Storage Performance Council (SPC) has introduced a new benchmark series, the SPC-1C/E, which provides detailed energy usage for storage subsystems. So far there have been only two published submissions in this category but we look forward to seeing more in the future. The two submissions are for an IBM SSD and a Seagate Savvio (10Krpm) SAS attached storage subsystems.
My only issue with the SPC-1C/E reports is that they focus on a value of nominal energy consumption rather than reporting peak and idle energy usage. I understand that this is probably closer to what an actual data center would see as energy cost but it buries some intrinsic energy use profile differences.
SSD vs Drive power profile differences
The deltas for reported energy consumption for the two current SPC-1C/E submissions show a ~9.6% difference in peak versus nominal energy use for rotating media storage. Similar results for the SSD storage show a difference of ~1.7%. Taking these results for peak versus idle periods, shows the difference for rotating media being 28.5% and for SSD, ~2.8%.
So, the upside for SSD is drive them as hard as you want and it will cost you only a little bit more energy. In contrast, the downside is leave them idle and it will cost almost as much as if you were driving them at peak IO rates.
Rotating media storage seems to have a much more responsive power profile. Drive them hard and it will consume more power, leave them idle and it consumes less power.
Data center view of storage power
Now these differences might not seem significant but given the amount of storage in most shops they could represent significant cost differentials. Although SSD storage consumes less power, it’s energy use profile is significantly flatter than rotating media and will always consume that level of power (when powered on). On the other hand, rotating media consumes more power on average but it’s power profile is more slanted than SSDs and at peak workload consumes much more power than when idle.
Usualy, it’s unwise to generalize from two results. However, everything I know says that these differences in their respective power profiles should persist across other storage subsystem results. As more results are submitted it should be easy to verify whether I am right.