The storage market is lighting up with discussion on this topic. Although I don’t think Shakespeare meant his famous quote to be modified in the context of storage, it does pose an interesting question. Should storage arrays shift to all-flash or to say true to disks? Let’s take a good look into this discussion with the things that we know.

  • Flash is 100x more expensive than hard-disk drives (HDDs) – Solid-state drives (SSDs), also known as flash, have come down in price quite a bit over the past few of years. So have disks, just not as drastically. If we compare SSDs and HDDs on a per-capacity basis, flash is still significantly more expensive than disk. Compare the price of 6TB of SSD to a 6TB 3.5-inch HDD and you’re closer to 100x more expensive!
  • Disk is 100x more expensive than flash – Yes, you read that right. I have completely contradicted myself; however, if we compare HDD to SSD on a per-IOPS basis, HDD is significantly more expensive. HDDs can only deliver modest IOPS. The allure of flash drives is the massive IOPS they can deliver. 

Based on those two points, we can consider HDD and SSD equal, or, significantly opposite, depending on your needs. If you only care about massive capacity, you should choose HDD solutions. If you only care about massive IOPS, stick with all-flash arrays. As long as you fall into one of those two categories, it’s a simple choice. But there is more to the story…let’s keep drilling down.

  • Disks are better optimized to handle sequential I/O (relational databases for example). Here’s a paradox! Cost per IOPS for disks is actually cheaper than SSD when workloads are sequential!
  • Flash is better optimized to handle random I/O (email for example) At this point, if you have a lot of sequential workloads taking up a lot of capacity, disk-based storage is best. On the other hand, if you have a lot of random workloads with a lot of IOPS, then flash should be the solution for you. Since you probably don’t fit neatly into these two categories, it’s likely that hybrid storage will be the best all-around solution.

Hybrid arrays, such as the new Lenovo Storage S2200 and S3200, can add SSD storage (between 5 and 10 percent) to a disk array and can produce almost 80 percent of the IOPS of an all-flash array. They do this by utilizing software features in the array called data tiering. Heavily accessed data is moved to the super-fast flash disks, and the less-accessed data is moved to the high-capacity drives, which are much cheaper. This means about 70 percent lower cost for 20 percent lower performance than an all-flash array. Additionally, you can get the benefits of both sequential workloads and random workloads all in the same array.

So, the answer to the question, “Should I flash or not flash?” is do both! Use flash for its performance benefits and use HDDs for their capacity benefits.