That whirring you hear when you boot your computer or when it wakes from sleep mode is the sound of your hard drive\u2019s magnetic disks beginning to spin. Conceptually not dissimilar to a record player, a hard disk drive (HDD) is an electromechanical device with an actuator arm that positions itself over spinning disks, called platters, in order to read or write information.\nWhile record players top out at 78 rpm, today\u2019s enterprise-grade HDDs can spin at 15,000 rpm. Even at that speed, however, there are unavoidable delays associated with heads finding the spot on the drive that contains the data being requested. And sometimes a drive may need to read from multiple locations in order to complete a command, multiplying wait times.\n\nBE SURE NOT TO MISS:\n\nWhy NVMe? Users weigh benefits of NVMe-accelerated flash storage\nWhat is hyperconvergence?\nMaking the right hyperconvergence choice: HCI hardware or software?\nWhat is a SAN and how does it differ from NAS?\n\n\nWhy solid state drives (SSDs) are better\nSolid state drives (SSD), as the name suggests, don\u2019t have moving parts or spinning disks. They use interconnected pools of flash memory that are managed by an SSD controller to deliver speeds far beyond what an HDD can offer.\nSome rough examples: SSDs can reduce boot time from around 35 seconds to about 10 seconds. Write speeds for an HDD might be in the range of 50-120Mbit\/sec. compared to between 200-500Mbit\/sec. for an SSD. An HDD might be able to complete between 50-200 input\/output operations per second, while a comparable SDD might be able to do as many as 90,000. And some enterprise grade, rack scale SSDs claim to be able to process millions of operations per second.\nSSD prices and reliability\u00a0\nBut despite their performance advantages, SSDs only have a 10% market share compared to HDDs for a couple of reasons. First and foremost, they\u2019re expensive. HDDs today average around 3-4 cents per GB, compared to 25-30 cents for SSDs. For example, a 1TB internal HDD costs around $40, while a comparable SSD costs around $250.\n[ Related: SSDs poised to get a lot cheaper\u00a0]\nThe second reason is that SSDs are quirky little devices that get slower as they fill up. And eventually, the flash cells reach a state where they can no longer complete write operations at all. SSD makers have created clever workarounds, including something called garbage collection, in order to mitigate this problem, and SSD vendors will tell you that today\u2019s devices have reliability and longevity equal to HDDs. But the perception lingers.\nOverall, the trendline for SSDs is certainly pointing up. On the consumer front, manufacturers are starting to make SSDs standard equipment on their higher end desktops and laptops. And that speed advantage is making SSDs desirable in cloud and enterprise scenarios where performance is paramount. Gartner is predicting that by 2021, 50% of data centers will use solid state arrays for high performance computing and big data workloads, up from less than 10% today.\nHow does an SSD work?\nA simple USB flash drive (or thumb drive) is an example of solid-state drive technology. An SSD is a larger, more complex device that aggregates pools of NAND flash storage, the type of storage also found in MP3 players and digital cameras. Unlike RAM, which doesn\u2019t retain data when the machine shuts off, SSD flash memory is non-volatile, which means data is retained whether the device is powered on or not.\nWith SSDs, every block of data is accessible at the same speed as every other block, no matter the location. This makes SSDs inherently faster than hard drives, where platters are spinning and drive heads are moving to the right location.\nWith HDDs, large files can be broken up and tucked into unused nooks and crannies of the drive, and data can be easily updated in place. This allows for efficient use of the total drive capacity. On the other hand, scattered data obviously takes longer to locate, which is why defragmenting a hard drive has become a standard part of device maintenance.\n Intel SSD DC P6400 Series\n\nIntel's SSD DC P6400 Series is a 3D NAND solid state drive designed for data centers\n\n\nSDDs have a different and bigger problem \u2013 SSDs can only write to empty blocks. That\u2019s okay when the SSD is new and all the blocks are empty. But over time, as blocks get filled up, overwriting data becomes an issue, because the only way an SSD can update an existing page is to copy the contents of the entire block into memory, erase the block and then write the contents of the old block in addition to the new data. If there are no empty blocks available, the SSD must scan for blocks marked for deletion, but not yet deleted, erase them, and then write the data to the now-erased page. Over time, as the SSD fills up, writing to the drive becomes more complicated and slower.\n[ Related: What is NVMe, and how is it changing enterprise storage\u00a0]\nSSDs use a combination of methods to overcome this problem, including overprovisioning; wear leveling, a type of load balancing for flash cells; and garbage collection, a process that works in the background to delete stale files and optimize the available space, similar to the defrag function in HDDs.\nSSD vs. HDD in the enterprise\nSSDs have a number of advantages over HDDs that can help offset the difference in sticker price. SSDs are quiet. They don\u2019t vibrate, which improves reliability. If dropped, a hard drive might get damaged; not so with an SSD. They use less power and generate less heat, which can add up to big savings in a large data center scenario. They are also smaller and more powerful than HDDs, so data centers can pack more storage into less space. And, of course, there\u2019s the speed advantage.\nSince HDDs have a massive installed base of customers who basically feel that disk drives are \u201cgood enough,\u201d the decision to go with a new and different technology requires that companies build a solid business case.\nCompanies need to conduct a detailed cost\/benefit analysis to determine whether a move to SSDs make sense. One deployment approach would be a slow migration where SSDs would be a requirement in new servers and storage devices. Another approach is to use SSDs exclusively for \u201cTier 0\u201d data in a tiered data storage scenario. Tier 0 data is transactional data requiring high performance, such as in financial or ecommerce applications.\nOther enterprise use cases for SSDs include ruggedized notebooks or laptops, applications where boot time is important, the editing of large media files like video and audio, cache drives and database servers.\nAt the same time that enterprises are thinking about SSDs vs. HDDs, it\u2019s important to note that the total volume of data is exploding, so most companies will continue to buy both types of drives for a very long time. In fact, IDC predicts that even as SSD sales volumes increase, solid-state drives will still only amount to 20% of total market share in the enterprise by 2025.