As the platters spin, HDD’s for cloud, virtual and traditional storage environments

July 19, 2013 – 2:30 pm

Storage I/O trends

HDDs for cloud, virtual and traditional storage environments

This is a follow-up to a recent series of posts on Hard Disk Drives (HDD’s) along with some posts about How Many IOPS HDD’s can do.

HDD and storage trends and directions include among others

HDD’s will continue to be declared dead into the next decade, just as they have been for over a decade, meanwhile they are being enhanced, continued to be used in evolving roles.

hdd and ssd

SSD will continue to coexist with HDD, either as separate or converged HHDD’s. Where, where and how they are used will also continue to evolve. High IO (IOPS) or low latency activity will continue to move to some form of nand flash SSD (PCM around the corner), while storage capacity including some of which has been on tape stays on disk. Instead of more HDD capacity in a server, it moves to a SAN or NAS or to a cloud or service provider. This includes for backup/restore, BC, DR, archive and online reference or what some call active archives.

The need for storage spindle speed and more

The need for faster revolutions per minute (RPM’s) performance of drives (e.g. platter spin speed) is being replaced by SSD and more robust smaller form factor (SFF) drives. For example, some of today’s 2.5” SFF 10,000 RPM (e.g. 10K) SAS HDD’s can do as well or better than their larger 3.5” 15K predecessors can for both IOPS and bandwidth. This is also an example where the RPM speed of a drive may not be the only determination for performance as it has been in the past.

capacity
Performance comparison of four different drive types, click to view larger image.

The need for storage space capacity and areal density

In terms of storage enhancements, watch for the appearance of Shingled Magnetic Recording (SMR) enabled HDD’s to help further boost the space capacity in the same footprint. Using SMR HDD manufactures can put more bits (e.g. areal density) into the same physical space on a platter.

capacity
Traditional vs. SMR to increase storage areal density capacity

The generic idea with SMR is to increase areal density (how many bits can be safely stored per square inch) of data placed on spinning disk platter media. In the above image on the left is a representative example of how traditional magnetic disk media lays down tracks next to each other. With traditional magnetic recording approaches, the tracks are placed as close together as possible for the write heads to safely write data.

With new recording formats such as SMR along with improvements to read/write heads, the tracks can be more closely grouped together in an overlapping way. This overlapping way (used in a generic sense) is like how the shingles on a roof overlap, hence Shingled Magnetic Recording. Other magnetic recording or storage enhancements in the works include Heat Assisted Magnetic Recording (HAMR) and Helium filed drives. Thus, there is still plenty of bits and bytes room for growth in HDD’s well into the next decade to co-exist and complement SSD’s.

DIF and AF (Advanced Format), or software defining the drives

Another evolving storage feature that ties into HDD’s is Data Integrity Feature (DIF) that has a couple of different types. Depending on which type of DIF (0, 1, 2, and 3) is used; there can be added data integrity checks from the application to the storage medium or drive beyond normal functionality. Here is something to keep in mind, as there are different types or levels of DIF, when somebody says they support or need DIF, ask them which type or level as well as why.

Are you familiar with Advanced Format (AF)? If not you should be. Traditionally outside of special formats for some operating systems or controllers, that standard open system data storage block, page or sector has been 512 bytes. This has served well in the past however; with the advent of TByte and larger sized drives, a new mechanism is needed. The need is to support both larger average data allocation sizes from operating systems and storage systems, as well as to cut the overhead of managing all the small sectors. Operating systems and file systems have added new partitioning features such as GUID Partition Table (GPT) to support 1TB and larger SSD, HDD and storage system LUN’s.

These enhancements are enabling larger devices to be used in place of traditional Master Boot Record (MBR) or other operating system partition and allocation schemes. The next step however is to teach the operating systems, file systems and hypervisors along with their associated tools or drives how to work with 4,096 byte or 4 Kbyte sectors. The advantage will be to cut the overhead of tracking all of those smaller sectors or file system extents and clusters. Today many HDD’s support AF however by default may have 512-byte emulation mode enabled due to lack of operating system or other support.

Intelligent Power Management, moving beyond drive spin down

Intelligent Power Management (IPM) is a collection of techniques that can be applied to vary the amount of energy consumed by a drive, controller or processor to do its work. These include in the case of a HDD slowing the spin rate of platters, however keep in mind that mass in motion tends to stay in motion. This means that HDD’s once up and spinning do not need as much relative power as they function like a flywheel. Where their power draw comes in is during reading and write, in part to the movement of read/write heads, however also for running the processors and electronics that control the device. Another big power consumer is when drives spin up, thus if they can be kept moving, however at a lower rate, along with disabling energy used by read/write heads and their electronics, you can see a drop in power consumption. Btw, a current generation 3.5” 4TB 6Gbs SATA HDD consumes about 6-7 watts of power while in active use, or less when in idle mode. Likewise a current generation high performance 2.5” 1.2TB HDD consumes about 4.8 watts of energy, a far cry from the 12-16 plus watts of energy some use as HDD fud.

Hybrid Hard Disk Drives (HHDD) and Solid State Hybrid Drives (SSDHD)

Hybrid HDD’s (HHDD’s) also known as Solid State Hybrid Drives (SSHD) have been around for a while and if you have read my earlier posts, you know that I have been a user and fan of them for several years. However one of the drawbacks of the HHDD’s has been lack of write acceleration, (e.g. they only optimize for reads) with some models. Current and emerging HDDD’s are appearing with a mix of nand flash SLC (used in earlier versions), MLC and eMLC along with DRAM while enabling write optimization. There are also more drive options available as HHDD’s from different manufactures both for desktop and enterprise class scenarios.

The challenge with HHDD’s is that many vendors either do not understand how they fit and compliment their tiering or storage management software tools, or simply do not see the value proposition. I have had vendors and others tell me that the HHDD’s don’t make sense as they are too simple, how can they be a fit without requiring tiering software, controllers, SSD and HDD’s to be viable?

Storage I/O trends

I also see a trend similar to when the desktop high-capacity SATA drives appeared for enterprise class storage systems in the early 2000s. Some of the same people did not see where or how a desktop class product or technology could ever be used in an enterprise solution.

Hmm, hey wait a minute, I seem to recall similar thinking when SCSI drives appeared in the early 90s, funny how some things do not change, DejaVu anybody?

Does that mean HHDD’s will be used everywhere?

Not necessarily, however there will be places where they make sense, others where either a HDD or SSD will be more practical.

Networking with your server and storage

Drive native interfaces near-term will remain as 6Gbs (going to 12Gbs) SAS and SATA with some FC (you might still find a parallel SCSI drive out there). Likewise, with bridges or interface cards, those drives may appear as USB or something else.

What about SCSI over PCIe, will that catch on as a drive interface? Tough to say however I am sure we can find some people who will gladly try to convince you of that. FC based drives operating at 4Gbs FC (4GFC) are still being used for some environments however most activity is shifting over to SAS and SATA. SAS and SATA are switching over from 3Gbs to 6Gbs with 12Gbs SAS on the roadmap’s.

So which drive is best for you?

That depends; do you need bandwidth or IOPS, low latency or high capacity, small low profile thin form factor or feature functions? Do you need a hybrid or all SSD or a self-encrypting device (SED) also known as Instant Secure Erase (ISE), these are among your various options.

Disk drives

Why the storage diversity?

Simple, some are legacy soon to be replaced and disposed of while others are newer. I also have a collection so to speak that get used for various testing, research, learning and trying things out. Click here and here to read about some of the ways I use various drives in my VMware environment including creating Raw Device Mapped (RDM) local SAS and SATA devices.

Other capabilities and functionality existing or being added to HDD’s include RAID and data copy assist; secure erase, self-encrypting, vibration dampening among other abilities for supporting dense data environments.

Wrapup, for now

Do not judge a drive by its interface, space capacity, cost or RPM alone. Look under the cover a bit to see what is inside in terms of functionality, performance, and reliability among other options to fit your needs. After all, in the data center or information factory not everything is the same.

From a marketing and fun to talk about new technology perspective, HDD’s might be dead for some. The reality is that they are very much alive in physical, virtual and cloud environments, granted their role is changing.

Ok, nuff said (for now).

Cheers gs

Greg Schulz – Author Cloud and Virtual Data Storage Networking (CRC Press), The Green and Virtual Data Center (CRC Press) and Resilient Storage Networks (Elsevier)

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