I ran some numbers (thanks to Engmyr’s assistance) regarding the various NetApp disk/shelf options. There are 3 main types of disk: 7.2k RPM SATA, 10K RPM SFF (Small Form Factor), and 15k RPM SAS. Each of these disks and options have different capabilities and benefits.
Let’s look first at IOPS/$1k, which is performance-per-dollar, so to speak:
The key takeaways here: SAS is always the best performance-per-dollar, and that 1TB SATA is actually better than 900GB SFF disks when it comes to performance-per-dollar.
Now let’s look at GB/$1k, which is storage-per-dollar:
The key takeaways: IF YOU NEED STORAGE, ALWAYS BUY THE BIGGEST DISK SIZE POSSIBLE, as they tend to be at a discount. It’s cheaper to buy 1x 3TB shelf rather than 3x 1TB shelves, and you also save on space, power, and cooling. In particular, the 2/3TB SATA and 600GB SAS options are your top 3 “bang for your buck” options, as they provide large storage-per-dollar increases. If you’re able to leverage FlashCache to soak up most of your IOPS load, you can take advantage of the massive storage-per-dollar savings of SATA. Note that SAS only beats SATA in performance-per-dollar at about a 3:1 ratio, while SATA betas SAS in storage-per-dollar at almost 4:1 ratios.
Now let’s look at IOPS/TB, which is based on your particular application/environment.
Clearly the SAS drives hold the lead here. If you look at how low the SATA drives are, it’s very clear that they provide only a fraction of the faster disks’ performance. Remember, though, that SATA drives also provide more storage, so the IOPS/shelf is actually much closer (around 1:3).
Finally, let’s look at density.
As you can see, the SFF drives, which fit 24 disks into 2U instead of 4U, lead the pack in terms of IOPS/U. If you need performance in a small footprint, they can provide it with less power/space than SAS. However, remember that SAS provides better IOPS/$1k and similar GB/$1k, so you’re essentially trading capital cost for opex cost. The SAS drives will be cheaper up front (capex) but will cost more to run in power/space (opex), while the SFF drives are the reverse. You’ll have to figure out the exact numbers to make the right choice for your customer.
Obviously the SATA drives give you only 1/3rd of SAS’ performance density but over 6x the storage density. SFF is a reasonable middle-ground here, providing the best performance density and between 50-100% of SATA’s storage density. It is right in the middle in terms of storage-per-dollar and performance-for-dollar. It’s not the best deal on either, but if space/power are at a premium, they have a great value proposition.
SFF is incredibly dense, middle of the road between GB/$1k and IOPS/$1k, good for a mixed workload
SATA is storage-dense but low-performance
SAS is performance-dense but low-storage
The 600 SFF option is the WORST upgrade, as it gives very little but for a big cost increase. The 900 SFF option is more reasonable, but the 1TB SATA option will give you better GB/$1k and IOPS/$1k, as long as space/power isn’t an issue. The 450 SFF option is really the most attractive of the SFF bunch. However, even then, the 600 SAS option is better than the 450 SFF option in EVERY way (IOPS/TB, IOPS/$1k, GB/$1k) outside of space/power. So, you want to get 600 SAS for high performance or 1TB SATA for storage, unless space/power is at a premium. If you don’t care about space/power, you’re better off with SAS/SATA, based on your workload.
NetApp would prefer that you simply try to match your SFF drives up with your exact IOPS/TB, but since the 600 SAS drives give you better IOPS/TB, the only driving force is space/power (opex).
The 3TB SATA upgrade is the cheapest upgrade around, and the 2TB upgrade is great as well. If you need low-IOPS storage, 2TB/3TB can be very attractive.
Shelves to buy:
VERY performance-heavy – 300/450 SAS (very high IOPS/TB)
Performance-based – 600 SAS (best) or 450 SFF (if space/power are an issue)
VERY Storage-heavy – 2/3TB SATA
Storage-based – 1TB SATA (reasonable) or 900 SFF (if space/power are an issue)
Don’t buy: 600 SFF (go bigger to 900 SFF for more space or smaller to 450 SFF for better performance)