Help Me Choose: Hard Drives and Solid-state Drives

As an enterprise systems user, you are most concerned about the security of your data and the reliability of the medium holding that data.

Dell puts its Enterprise Hard Drive and Solid State Drive offerings through a rigorous validation process before they are ever considered as additions to our line of server and storage systems. Dell has stringent drive specifications for performance, duty cycles, Mean Time Between Failure (MTBF) and rotational vibration, which are all necessary for an Enterprise-level environment .These types of exacting specifications must be met before we will make them available for customer usage.

Performance and Cost varies among the different HDD and SSD offerings. Please refer to the individual tabs below to assess the impacts in your applications.

Hard Disk Drives (HDD) and Solid State Drives (SSD) come in several varieties designed to address differing enterprise customer needs. These include:

Solid State SAS and SATA Drives:
Fast storage medium for random IO

10K & 15K SAS Hard Drives:
Performance and availability for performance optimized applications

7.2K SAS & SATA Hard Drives: High capacity and exceptional $/GB for capacity optimized applications

Entry Drives: Least expensive drives used in applications where low usage and limited total number of drives are applicable. Due to restrictions on use, these drives are available in a small number of systems and configurations.

ISE – Instant Scramble Erase, New Feature as Standard Offering in 14G

  • The industry standard documents use the words “cryptographic” or “crypto.” Informally, people use the terms “instant erase,” “instant secure erase,” “instant scramble erase,” and others. For the purposes of retiring or repurposing function (system or array), capabilities in 14G exist to optionally permanently erase customer content from Hard Disk Drives (HDDs) and Solid State Drives (SSDs)
  • Drive data erasing is categorized as either:
    • Overwrite – Erase by writing 0s across the drive (this takes time dependent upon drive capacity size).
    • Scramble – Erase using a cryptographic erase supported by the drive. ISE drives automatically encrypt data using an internal media encryption engine and an internal data encryption key. This type of drive supports the T10 or T13 cryptographic sanitize commands, which Dell calls the “Instant Scramble Erase” feature, but does not support TCG functionality.
  • How ISE Works: Of course, if that is what you want to do, you now have a simple way of making all data on the drive unusable. You tell the drive to permanently throw away its hidden internal media encryption key, to self-generate a new, unrelated key, and then to start using the new key with its internal encryption/decryption engine. From that point forward the data already on the media is useless (“scrambled”). The drive now uses the new internal media encryption key for its transparent encryption and decryption. That’s how ISE works
  • ISE Benefits:
      • Speed – executes fast, compared to a single-pass full disk write of 8 hours or more for a 4 TB HDD
      • Consistency – the time to scramble is independent of the drive’s storage capacity
      • Simplicity – uses a standard command; no specialized security command protocol is used
      • Thoroughness – even physical locations of reassigned logical blocks are scrambled (in the rare chance that data can be somehow recovered from these “bad” locations). The next best practice for “erasing” a HDD (overwriting the entire drive several times) cannot touch these physical locations.
      • User Confidence – once they understand how ISE works and how the strong 256-bit AES encryption protects their data, customers may be more willing to return drives for FA (Failure Analysis)
      • Repurposing – drives can be quickly “recycled” into new uses in the data center with no residual data from previous use

Hard Disk Drives for Dell Enterprise server and storage products are available in several different types, including Mission Critical (10K & 15K) Performance Optimized, Business Critical (7.2K) Capacity Optimized.

Generally speaking, the Mission Critical (MC) or Performance Optimized drives (10K and 15K SAS) are used in those application requiring the highest reliability and performance and are only available in the 2.5” small form factor. Business Critical (BC) or Capacity Optimized drives (7.2K Nearline SAS and SATA) may provide much higher capacities, but lower reliability and performance when compared to Mission Critical. They are available in both 2.5” small form factor and 3.5” large form factor. There is a fundamental transition occurring in the HDD industry. The standard size of a basic unit of data (a sector on the drive) is changing from 512 bytes to 4K bytes. Fortunately there are ways to maintain the 512 byte sector size, so that both are available into the future. Below is information on that addition and what a user should consider:

  • Beginning in late 2009, accelerating in 2010, and hitting mainstream in 2011 for client-based HDDs, hard drive companies began migrating away from the legacy sector size of 512 bytes to a larger, more efficient sector size of 4,096 bytes, generally referred to as 4K sectors, and now referenced as Advanced Format by IDEMA (The International Disk Drive Equipment and Materials Association). Enterprise HDDs are also moving to embrace this format, but will be slower to adopt. The first Advanced Format enterprise HDD became available in 2012, with a limited set in 2013 and a more general distribution in 2014 and beyond.
  • Customers have been using applications and operating systems / file systems built on 512 bytes (512n) for decades. This move to 4K byte sector size will impact those software stacks and will result in additional validation work as well as possible structural changes to software as the transition is made. New, higher capacity drives will need to be created in this 4K format. Recognizing that customers may be reluctant to make a change like this quickly, an emulation model of these drives has been created – the drive is built from 4K technology, but allows for 512 byte addressing and transfer at the interface. These drives are known as 512e.
  • Below is a table describing these concepts:

Format type

Bytes per sector value

Bytes per physical sector value










  • There are many aspects of modern computing systems that continue to assume that sectors are always 512 bytes. The Dell HDD offering contains 512n drives, 512e drives, and drives in the 4Kn format. The 512n format is available for customers interested in maintaining the same drive type they have used over time. The 512e drives provide a 512 byte sector size for those capacities not available in 512n. The 4Kn formatted drives are for those customers interested in adopting the latest, highest capacity HDDs and for those getting prepared for the future direction of the HDD industry. Note that 512 byte/sector addressing will continue as a recognized and supported format for many years into the future. The share of drives formatted as 4Kn could continue to remain small and the newest, highest capacity HDDs now and on the roadmap will also be available in 512e sector format.

Enhanced Performance 512e HDD as New Offering in 13G & 14G

  • In late April 2017, Dell has introduced a new 2.5” form factor 900GB 15K 512e 12Gbps SAS HDD with Enhanced Cache to boost Read performance in addition to the Advance Write Cache that comes standard in this family. TurboBoostTM (trademark of Seagate Inc) Enhanced Cache was Seagate’s major performance enhancement to standard enterprise performance HDD design (10K & 15K RPM rotational speed). This new 512e drive integrates small amount of eMLC NAND as cache, reducing latencies for significantly faster, predictable response times. Rather than constructing storage solutions with a mixture of discrete HDDs and SSDs, TurboBoost can often provide the best of both worlds. At the very least, TurboBoost can help to improve general work productivity through greatly improved availability of hot data (the data most frequently sought by the host) and greatly reduced IOPS response time.
    • Hot data gets copied from magnetic media into NAND cache. Subsequent requests for this data by the host can then be fulfilled far faster from flash memory than from rotating magnetic platter (media/disk). As the cache fills up, the least hot files will retire from NAND to make room for more data while the original files remain accessible from the disk media if needed. With TurboBoost technology, the seek and rotational latency part of a conventional drive’s read process often vanish, because if data resides in NAND, there is no spinning media to navigate.
  • Enhanced cache HDD benefits vary by applications - the greater the workload, the more effective they are. Ideal for building new high-performance servers, manage multiple transactions quickly, or drop-in replacements as the feature is active full time and does not require any enablement from host.
    • Virtual Desktop Infrastructure (VDI)
    • Online Transaction Processing (OLTP)
    • Webservers
    • Small Database Query
    • Exchange Workloads
    • Random Read/Write Tasks

For more detail on sample performance results per drive capacity, please view this comparison document.

Dell offers different solid-state drive (SSD) solutions to meet different customer needs. Enterprise SSDs as a class are unique compared to client or consumer-based SSD in terms of reliability, performance and architecture. While consumer-based SSDs, such as those utilized in notebooks are designed with a focus on consumer-based workloads, rigidity and battery life, enterprise-class SSDs are designed around enterprise application I/O (input/output) requirements with focus points of random I/O performance, reliability, and protection of data during a sudden power-down.

Understanding the basics of enterprise-class SSDs allow customers to make informed decisions when comparing solutions:

Over-provisioning: The Achilles' heel of SSDs are their write characteristics. To rewrite an area of an SSD that has already been written, the data must be erased and then written. In order to overcome a portion of the write performance penalty, Dell enterprise SSDs found across Dell PowerEdge products, all employ a practice known as over-provisioning of Flash. This practice keeps native Flash capacity beyond the user-defined capacity, and utilizes the additional space as a scratch pad of sorts to quickly put down application write data on areas of Flash that are already in an erased state. The SSDs perform cleanup functions of this over-provisioned Flash space during time periods typically not impacting application performance.

Write Endurance: Write endurance is the number of program/erase (P/E or write cycles) that can be applied to a block of flash memory before the storage media becomes unreliable. Due to different data center workloads and read/write needs, Dell offers different enterprise SSDs with different endurance ratings so customers can design the right solution for their needs.

Below are the different categories (swim lanes) of enterprise SSDs Dell offers:
    Write Intensive (WI) - 50/50 read/write workloads with highest endurance. HPC, Database logging, and caching are example workloads. 
    Mix Use (MU) - 70/30 read/write workloads with medium endurance. E-mail/messaging, OLTP, and E-commerce are example workloads. 
    Read Intensive (RI) - 90/10 read/write workloads with lower endurance. Database warehousing, media streaming, and VOD solutions are example workloads. 
    Boot Optimized (Boot) - Lowest cost/small capacity SSDs designed to be used as a boot device in servers. Low endurance.
    Host Interface - Dell enterprise SSDs support three kinds of host interface options:
    SATA SSD - SATA SSDs are based on the industry standard SATA interface. SATA SSDs provide reasonable performance for enterprise servers.
    SAS SSD - SAS SSDs are based on the industry standard SAS interface. SAS SSDs combine superior reliability, data integrity, and data fail recovery making them suitable for enterprise applications.
    PCIe SSD - The Dell PowerEdge Express Flash PCIe SSD is a high performance solid state storage device that enables IOPS performance of up to 2000X more than conventional rotating hard drives.

For more detail on sample performance results per drive capacity, please view this comparison document.