Tag Archives: MAID

Hard Disk Drives (HDD) for virtual environments (Part IV) from power to warranties

StorageNetworkingBy 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

Hard Disk Drives (HDD) for virtual environments (Part III) from form factor to power

StorageNetworkingBy Greg Schulz, Server and StorageIO @storageio

In part II of this series we covered some of the differences between various Hard Disk Drive (HDD) including looking beyond the covers at availability, cache and cost. Let us pick up where we left off on our look beyond the covers to help answer the question of which is the best HDD to use.

Form factor (physical attributes)

Physical dimensions including 2.5” small form factor (SFF) and 3.5” large form factor (LFF) HDDs. 2.5” HDDs are available in 7mm, 9mm and larger 14mm height form factors. Note that taller drives tend to have more platters for capacity. In the following image note that the bottom HDDs is taller than the others are.

Hard Disk Drive Sizes
Top thin 7mm, middle 9mm, and bottom 15mm (thick)

The above tall or “thick” (not to be confused with thick or thin provisioned) is a SFF 5.4K RPM 1.5TB drive that I use as an on-site backup or data protection target and buffer. The speed is good enough for what I use it for, and provides good capacity per cost in a given footprint.

Also, note that there is a low profile 7mm device (e.g. middle) that for example can fit into my Lenovo X1 laptop as a backup replacement for the Samsung SSD that normally resides there. Also shown on the top is a standard 9mm height 7.2K Momentus XT HHDD with 4GB of slc nand flash and 500GB of regular storage capacity.

Functionality

Functionality include rebuild assist, secure erase, self-encrypting device (SEDs) without or without FIPS, RAID assist, support for large file copy (e.g. for cloud, object storage and dispersal or erasure code protection). Other features include intelligent power management (beyond first generation MAID), native command queue (NCQ), and Advanced Format (AF) 4Kbyte block and 512 byte emulation). Features also include those for high-density deployments such as virtualization and cloud such as vibration management in addition to SMART (Self-Monitoring, Analysis, and Reporting Technology) reporting and analysis.

Drives can also depending on vendor, make and model support various block or sector sizes including standard 512, 520, 524 and 528 for  different operating systems, hypervisors or controllers. Another feature mentioned above is the amount of volatile (DRAM) or persistent (nand flash) cache for read and read-ahead. Some drives are optimized for standalone or JBOD (Just a Bunch of Disks) and others for use with RAID controllers. By the way, put several SSD drives into an enclosure without a controller and you have Just a Bunch Of SSDs or JBOS.  What this means is that some drives are optimized to work with RAID arrays and how they chunk or shard data while others are for non-RAID use.

Speaking of RAID and HDDs, have you thought about your configuration settings, particular if working with big data or big bandwidth and large files or objects? If not you should including paying attention to stripe, chunk or shard size of how much data gets written to each device. With larger IO sizes, revisit what the default settings are to determine if you need to make some adjustments. Just as some drives are optimized for working with RAID controllers or software, there are some drives being optimized for cloud and object storage along with big data applications. The differences is that these drives are optimized for moving larger chunks or amounts of data usually associated with distributed data dispersal, erasure coding and enhanced RAID solutions. An example of a cloud storage optimized HDD is the Seagate Constellation CS (Cloud Storage).

Moving on, some drives are designed to be spinning or in constant use while others for starting and stopping such as with a notebook or desktop. Other features appearing in HDDs support high-density, along with hot and humid environments for cloud and managed service provider or big data needs. The various features and functionality can be part of the firmware enabled for a particular device along with hard features built into the device.

Interface type and speed

The industry trend is moving towards 6Gb SAS for HDDs similar to that for SSD drives. However, there is also plenty of 6Gb SATA activity, along with continued 4Gb Fibre Channel (4GFC) that eventually will transition to SAS. There is also prior generation 3Gb SAS and 3Gb SATA and you might even have some older 1.5Gb SAS or SATA devices around, maybe even some Parallel ATA (PATA) or Ultra320 (Parallel SCSI). Note that SATA devices can plug into and work with SAS adapters and controllers, however not the other way around.

Note that if you see or hear about a storage system or controller with back-end 8Gb Fibre Channel, chances are the HDD would auto-throttle negotiate down to 4GFC. In addition to the current 6Gb speed of SAS, there are improvements in the works for 12Gb and beyond, along with many different topology or configuration options. If you are interested in learning more about SAS, check out SAS SANs for Dummies sponsored by LSI that I helped write.

Notice I did not mention iSCSI, USB, Thunderbolt or other interfaces and protocols? Some integrators and vendors offer drives with those among other interfaces, they are usually SAS or SATA with a bridge, router or converter interface attached to them externally or as part of their packaging (See following image).

Performance of the device

A common high-level gauge of drive performance is the platter rotational speed.  However there is other metrics including seek time, transfer rate and latency. These in turn vary based on peak and sustained, read or write, random or sequential, large or small IOPS or transfer requests. There are many different numbers floating around as to how many IOPS a HDD can do based on its rotational speed among other factors. The challenge with these numbers or using them is putting into context of what size the IOP is, was it a read or write, large or small, random or sequential relative to your needs. Another challenge is how those IOPs are measured, for example were the measured below a file system to negate buffering, or via a file system.

Rotational speed such as 5,400 (5.4K) revolutions per minute (RPM), 7.2K, 10K and 15K RPMs. Note that while a general indicator of relative speed, some of the newer 10K SFF (e.g. 2.5”) HDDs provide the same or better performance of earlier generation 3.5” 15K devices. This is accomplished with a combination of smaller form factor (spiral transfer rate) and improvements in read/write electronics and firmware. The benefit is that in the same or smaller footprint, more devices, performance and capacity can be packaged as well as the devices individually using less power. Granted if you pack more devices into a given footprint, the aggregate power might increase, however so too does the potential performance, availability, capacity and economics depending on implementation. You can see the differences in performance using various HDDs including an HHDD in this post here that looked at Windows impact for VDI planning.

This wraps up this post, up next part IV, we continue our look beyond the covers to determine the differences and what HDD is best for your virtual or other data storage needs.

Ok, nuff said (for now).

Cheers gs