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Overview

Selecting an appropriate drive technology for a dedicated server can be somewhat challenging, particularly considering the many available options in terms of capacity and drive type. On this page, we explore various significant factors, and also provide some information on specific performance attributes, to help you more effectively decide what drive technology is best for your dedicated hosting needs.

SATA vs. SCSI

One of the most prevailing misconceptions regarding the SATA and SCSI drives is that the primary difference is in the way the drives interface to a computer. Although they are of course different in that respect, the more fundamental differences have to do with specific aspects of construction of the drive -- specifically, the mechanics, materials, electronics, and firmware. Thus, the true distinction is between Personal Storage (or "PS") drives and Enterprise Storage (or "ES") drives. In almost all circumstances, SCSI drives are ES devices, while SATA drives are PS devices. Following is an overview of some of the fundamental differences:

PS vs. ES (SATA vs. SCSI): Design Considerations

It can be quite convincingly argued that the single most significant aspect to a PS drive is that its cost is roughly proportional to the cost of the overall computer system in which it is utilized. This can be easily seen by considering that an entire computer system, with 80GB of hard drive capacity, can be procured for approximately the same price as a 73GB 15,000 RPM Enterprise Storage drive. Simply put, cost pressures assure that PS drive design is dominated not by high reliability, but by high affordability. That's not to say that PS drives aren't suitable for their purposes, but it does indicate that they will not have the same quality characteristics as an ES drive.

ES (SCSI) drives on the other hand, have consistently been used on large computer systems. They thus reflect qualities that make them suitable for aggregation (i.e. group configurations), that make them optimised for randomly accessing small portions of data (typical "server" behaviour), and that make them intrinsicly reliable. Indeed, as one group of researchers succinctly put it, in a commercial environment, "[drive] failure could idle a considerable number of employees and directly impact business operations."

Following is a brief table that gives a summary of some of the more specific differences between drive types:

 
Personal Storage
Enterprise Storage
Rotational Latency Lower media spin speeds result in comparatively higher latency vs. ES drives. Innovation tends to focus on cost savings (e.g. lowering the net cost to make a 7,200 RPM motor). Higher spin speeds result in lower latency vs. PS drives. Innovation tends to focus on new technologies (e.g. building a 15,000 RPM motor for the first time).
Aggregation (i.e. > 1 drive) Designed for single-drive systems. Not as effective handling of rotational vibration, causing performance loss in multi-drive configurations. Designed for multiple-drive systems. Internal drive mechanisms better handle rotational vibration, thus avoiding related performance loss.
Drive Mechanics Lower-cost components, lower-power requirements lead to simpler but less failure-proof designs. Goal is to achieve 1,000,000 hours between failures, and to compensate for higher spindle speeds and other effects such as rotational vibration. More effective cooling, environmental protection built into the drive, O-ring sealed spindle motors, dessicant to control humidity, etc., are present.
Drive Electronics Simpler IDE/SATA interface allows for less complicated electronics, but this also translates to less performance gain at the firmware level. SCSI/FC drives typically have two processors; one for the servo, another for interface and read/write handling. ES drives also tend to have larger SRAM space, flash memory, data SRAM and cache SRAM.
Manufacturing Much more basic manufacturing and post-manufacture testing than Enterprise Storage drives. Significantly longer build and test times compared to PS; not only ensures reliability but improves performance as drive "learns" of track irregularities and media flaws.
Performance Characteristics Tends to use a larger number of drive platters / sacrificing performance to gain capacity. Lower RPM and larger platter sizes than ES degrade performance. Small drive platters, higher RPM, lead to better intrinsic performance. Aggressive seek scheduling improves performance and lowers mechanical duty cycle.
Rotational Vibration Since not normally designed for multi-drive use, rotational vibration (from the spinning of other drives within the chassis) throws drive actuator "off-track" -- causing aborted writes + failed seeks (and in extreme cases, inoperability). Explicitly designed to operate in close proximity to other spinning drives. External rotation detection can compensate in servo processing; combined with better build quality, this ensures lower performance loss from rotational vibration.
Intrinsic Reliability Reliability specifications designed for expected power-on-hours of 8 hours/day, 300 days/year. Using in a 24/7/365 server environment forces drive to work beyond specifications. Reliability specifications based on 24/7/365 drive use. Better scheduling algorithms also contribute to lower duty cycles, by making more efficient use of drive mechanics. Designed for enterprise-grade storage.

Choosing a Drive for your Dedicated Server

Of course, given the above, we normally recommend an enterprise-grade drive technology for dedicated server use. However, when reliability and efficiency are not major concerns, PS drives (SATA-based) can be effectively utilised, and do in fact enable higher-capacity-per-dollar-spent.

Seagate Cheetah - 15,000 RPM Drives

These are the cornerstone of our VPS hosting platforms, and of course are available for dedicated hosting clients. These drives hold a variety of distinctions, including:

  Being the first drive to break the 100-Mbyte/s sustained transfer rate barrier (peaking at 125 Mbytes/s)

  Perpendicular recording enables capacity up to 300GB while offering 30% higher performance.

  30% higher IOPS and more than 20% faster response times when compared to 3.5" 10,000 RPM drives.

  Highest reliability of any 3.5" drive in the industry, with a 0.62% Annualized failure rate.

  A focus on reliability and data protection has led to innovations that have improved the nonrecoverable error rate by a factor of 10 over earlier models.

  Exclusive IRAW (Idle Read After Write), Error Correction Code and second generation Background Media Scan significantly improves performance and reliability.

  Average Read/Write (msec) - 3.5/4.0

  Nonrecoverable Read Errors per Bits Read - 1 sector per 1016

10,000 RPM vs. 15,000 RPM Seagate Cheetahs

Following are specification comparisions for both the Seagate Cheetah 10K and 15K. This data is based on information provided by Seagate:

  Cheetah 10K Cheetah 15K
Spindle Speed10,000 RPM15,000 RPM
Average Read/Seek Time (msec) 4.75/5.33.5/4.0
Transfer Rate (sustained Mbytes/s) 39 to 8073 to 125
Nonrecoveral Read Errors per Bits Read 1 sector per 10151 sector per 1016
Annualized Failure Rate 0.62%0.62%
Performance (IOPS)
Based on a 14 drive clustered configuration
725955 (32% faster)
Response Time
Based on a 14 drive clustered configuration
22.1ms16.7ms

 
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