Drive Development

We have plans to tell you about promising and interesting drives of the future, so a brief overview and a little systematization will be useful. Storage systems are a separate area that is secondary to storage media, so we will not touch on it now. Strongly in the past, too, there is no need, let's get by with SATA / SAS at times, the latest history, the near future and beautiful pictures with numbers.

Back in the days of IDE disks, there was a need for inexpensive, albeit slow, high-volume storage. For this, buffered backplanes were invented to support hot swapping and other crutches to work with an interface that was not intended for this. The transition to SATA greatly facilitated the life of everyone - a compact golden finger connector instead of a terrible needle, support for hot swapping is laid down in the standard, simplification of cable management, can not be considered all the advantages. SATA A little later, the SAS standard appeared, which abolished the division into SCSI / SATA and unified the connection of all drives in a single connector. Universal SAS Connector









For quite some time, conventional SATA disks were massively used; division into desktop and corporate series did not exist yet. Unlike SCSI disks, SATA were designed to work one thing in the system and compatibility with RAID controllers left much to be desired. The manufacturers of the controllers were forced to compile multi-page compatibility lists with disks that were outdated with the release of new firmware. Our production also spent a lot of effort.

SAS disks of these shortcomings were deprived, but cost (and cost) much more per gigabyte of capacity. SAS 15K Performance also varied drastically (picture taken from our SAS vs SATA article ): File server test









Life was simplified when the first corporate discs were released. At first, they differed only in firmware and it was possible to alter “desktop” disks, but this was already a lot - compatibility problems became an order of magnitude less. Now corporate series differ from the usual ones not only in firmware, but also in the element base. More reliable engines, bearings, head drives, all this significantly affects the reliability and stability of the drive.

What did it affect?

Spindle revolutions, rpm	5200-7200	7200	10-15K
Reliability (MTBF), hours	600,000	1,200,000	1,600,000
Work load	Low (<10%)	Low / Medium (<20%)	High (100%)
Data integrity	Parity check	EDC + (ECC)	EDC / ECC + own protection
Vibration resistance, rad / s2	6	12.5	> 21
Error correction	Common for SATA	SATA + time control	Sense Keys, Codes, FRUs
Firmware / Functions	SATA	SATA + NL Feature Set	SCSI + Advanced Features (Dual Processors)
Unrecoverable Error Level	1 * 10 ^ -14	1 * 10 ^ -15	1 * 10 ^ -16
MTBF, hours per year	2400	8760	8760
Multi host	not	not	16 hosts at a time
T10 data protection	not	not	Yes

Vibration resistance greatly affects disk performance: By the way, here is a live demonstration of the effect:






The level of unrecoverable errors affects the reliability of work in arrays. Without delving into math, a 4000GB drive contains 8/25 * 10 ¹⁴ bits. Rebuilding RAID5 from 5 disks means transferring 40/25 * 10 ¹⁴ bits - when using regular disks, such an error will almost always occur, and this will result in an array collapse and data loss. Corporate drives reduce this chance by an order of magnitude, mission critical - by two.

At the same time, SAS disks began to spread in 2.5 "format. In 3.5" format, SAS disks remained only with a spindle speed of 15K revolutions, and 2.5 "again brought division by 10 / 15K. The development of 3.5" lines was decided to stop, so their performance has long been not changed. Due to the development of technology, 2.5 "15K drives outperform the old 3.5" 15K,www.etegro.ru/articles/sff-compare SAS SFF 2.5 inches At the same time, performance and SATA drives also increased, plus NL SAS, 7.2K disks with a different interface appeared. It seems to be a trifle, but along with this, many functions have appeared that directly affect performance. The difference The performance results of modern disks: Access with random addressing As you can see, the “simple” change of interface gave a performance increase of up to 20%. This is not counting the normal operation in storage systems, which got rid of the interposers with their added glitches. The findings on rotating media disks have not changed over the years, SAS disks are oriented to speed-sensitive tasks and requiring multi-threaded access:

• DBMS
• Highly loaded WEB-servers;
• ERP systems;
• systems for working with a large number of users - terminal servers, remote access servers.

SATA drives are required for tasks associated with large amounts of information. Among the common tasks successfully solved by SATA disks, the following can be distinguished:

• streaming operations, for example, video encoding;
• Data Warehouses
• backup systems;
• voluminous, but not loaded file servers.

In the next article, we will raise the topic of SSDs, their subspecies and unusual members of the family.