By Greg Schulz, Server and StorageIO @storageio
Let us pick up where we left off in part III in our look beyond the covers to help answer the question of which is the best HDD to use.
Power and energy
Power consumption will vary based on size and type of HDD, along with different usage. For example, during power-up there is a larger amount of energy being used vs. when the drive is idle (not reading or writing) yet still spinning, or actively reading and writing. With intelligent power management (IPM), inactive drives can go into lower power usage modes with variable performance. IPM includes the ability to vary the amount of power used to level of performance with different steps or levels. This is different from some first generation MAID solutions based on desktop class drives that were either on or off with subsequent performance issues. While an HDD requires power to spin the platters, once those are in motion, less power is required; however, energy is needed for the read write heads and associated electronics.
This leads to a common myth or misperception that HDDs consume a lot of energy because they are spinning. There is energy being used to keep the platters moving, however power is also required for the electronics to manage the drives interface, read write heads and other functions. With IPM leaving the drive spinning or reducing the rotational speed can help save power, so to can disabling or putting into low power mode the associated processors and control electronics.
As a comparison SSD, drives are often touted as not drawing as much energy compared to an HDD, which is true. However, SSDs do in fact consume electricity and get warm as they also have electronics and control processors similar to HDDs. If you do not believe this, put an SSD to work and feel it over time as it heats up. Granted that is an apple to oranges comparisons, however my point is that there is more to energy savings with HDDs than simply focusing on the rotational speeds. Speaking of energy savings, typical enterprise class drives are in the 4 to 8 watts or a fraction of what they were only a few years ago. Notebook, laptop and workstation drives can be in the single watt to a few watts in power usage range. Note that these numbers may be less than what some will talk about when comparing SSD and HDDs, or trying to make a point about HDDs and power consumption. The reason is this is a reduction from where just a few years ago when drives were in the “teens” in terms of watts per drive. For performance or active drives, compare those on a cost per activity per watt such as cost per IOP per watt, for inactive data then cost per capacity per watt can be relevant.
Security
Given the large amount of data that can be stored on an HDD along with compliance and other concerns, drive level security is becoming more common. There are different types of drive level encryption including self-encrypting devices (SEDs) with some supporting FIPS level requirements. Drive level encryption depending on implementation can be used to off-load servers, workstations or storage systems from performing encrypt and decrypt functions.
Space capacity
The space capacity of the drives is determined by the aerial density (how many bits in a given amount of space) per platter, the size of the platter (3.5” are larger than 2.5”) and number of platters. For example at the same aerial density, more bits and bytes exist on a 3.5” vs. 2.5” device, and by adding more platters (along with read/write heads) the resulting taller height drive has even more space capacity. Drive space capacities include 4TB and smaller for 3.5” devices and TB plus sized for various 2.5” form factors. Watch out for “packaging” games where for example a drive is offered as say 4TB that are actually two separate 2TB drives in a common enclosure (no RAID or NAS or anything else).
The super parametric barrier effects keeps being delayed, first with perpendicular recording, now with shingled magnetic recording (SMR) and heat assisted magnetic recording (HAMR) all in the works. The super parametric barrier is the point where data bits can no longer safely (with data integrity) be stored and later used without introducing instability. Watch for more on SMR and HAMR in a later post when we look at new and emerging trends.
Speaking of space capacity, ever wonder where those missing bits and bytes disappeared on a HDD or SSD? First there is how it is measured, meaning decimal or base10 vs. binary base 2 for example one Gigabyte (GB) being one billion bytes vs. 1,024,000,000.00 bytes. These space capacities are before RAID or hypervisor or operating system and file system formatting overhead are added. There is also reserved space for bad block re vectoring which can be thought of as hot spare blocks for when the drive (HDD or SSD) detects something going bad. In addition to the bad block areas, there are also some reserved space that you will not be able to access that is kept for drive management, read/write head alignment and other things.
Speaking of large capacity drives, as mentioned earlier, rebuild operations with RAID configurations can take longer given more data to move. Good news is that some RAID systems or solutions can rebuild a 1TB or 2TB drive as fast as or faster than a 9GB drive from a decade ago. The catch is that there are more drives and they are getting larger with 3TB and 4TB shipping and larger ones in the works. Things you can do to minimize the impact of long rebuild times; include selecting the right type of drive that has better endurance, reliability and availability. This could mean that selecting a lower priced drive up front that is not as reliable could cost you down the road. Configuration including RAID level, number of parity drivers, and software, adapter, controller or storage system with ability to accelerate rebuilds can also make a difference.
Another impact of large capacity drives or large numbers of HDDs in general is how to securely erase them when decommissioning. That is assuming you are securely erasing them or taking other safeguards disposition vs. throwing in the garbage or giving them away. Self-encrypting devices (SEDs) normally associated with security can be part of a solution for some environments. Since SEDs can effectively erase the data stored on those by, removing the enablement key, instead of hours or days, for some environments secure erase can be in minutes or less.
Warranties
There are various warranties on HDDs, those from the manufacture that may be the same as what an OEM or system integrator passes on to their customers. Some HDDs have a manufactures limited warranty of five years while others have shorter terms. Thus while a manufacture may offer a five year warranty, it can be up to the OEM or integrator to pass that warranty on, or in turn provider a shorter duration with different terms or price. Something to think about in terms of HDD warranties is that replacing them can mean sending your old device back in exchange for a new one. If you have sensitive or secure data on those devices, how will they be disposed of? An option is to not leverage return to vendor or manufacture warranties opting for self-disposition, or using self-encrypting devices (SEDs).
This wraps up this post, coming up next in part V we will look at what to use when, where along with other options and some trends.
Ok, nuff said (for now).
Cheers gs