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Due to SSD read/write latency and iops (I/O per
Second) These two aspects have about three orders of magnitude advantage over traditional mechanical hard drives, which has led some people to doubt the prospect of mechanical hard drives, I think SSD will be the first choice in the cloud computing era and will completely replace the mechanical hard drive. However, as the king of the era of mechanical hard drive, Seagate remains confident in the hard drive, in addition, 2.5 inch momentus adopting hybrid technology are released recently.
XT Series Hybrid hard drive products, mainly used for laptops.

 

Introduction

Currently, the momentus XT Series hard drive has three capacity configurations: 250 GB, GB, and GB. Based on the hard drive, the 4 gb slc is loaded.
Nand flash memory and 32 mb ddr cache. And supports "Adaptive"
Memory (Adaptive Memory) is a new technology that can automatically move frequently accessed data to the flash storage area to enable momentus
XT Series hard disks can improve the performance. The prices for 250 GB, 107 GB, and 115 GB are USD 137, USD, and USD respectively.

Figure 1. momentus XT concept diagram (derived from parameter [1])

 

Technical Features

In terms of technology, first of all, the momentus XT Series adopts the hybrid mode (Figure 1), that is, adding 4 GB of memory to the original 32 mb ddr cache of the hard disk and 4 GB of mechanical hard disk
The slc nand flash memory is used to store data that requires frequent access. In addition, there have been products similar to the hybrid architecture in the market, such as enterprise-level storage EMC tiered
Storage (Hierarchical Storage) technology (figure 2)
Channel) and SATA hard disks are added based on the flash disk, that is, the nand flash memory. This kind of hybrid design has the advantage of reducing access latency and improving the overall iops by adding the NAND memory.

Figure 1. Hierarchy of momentus XT

Figure 2. Tiered storage hierarchy

Second, momentus XT comes with "Adaptive"
Memory Technology, in fact, this technology has already appeared in both the enterprise storage industry and the civil industry. In the enterprise storage industry, there is EMC's fully automatic
Storage Tiering, fully automated storage Tiering) technology, with Lenovo's TSI (rapiddrive) technology in the civil industry.

In general, this hybrid design and "Adaptive Memory" technology have already been implemented, but only Seagate has been shipped in the form of a 2.5-inch hard disk this time.

 

Performance

Performance Testing

Is the hard drive test data of the momentus XT Series,

Figure 3. read/write speed test data (parameter [1])

The reading speed can reach 90 MB per second, and the writing speed can reach MB per second, but the momentus series with no built-in SSD are very similar in terms of reading and writing performance, in terms of reading and writing, it is 86mb and 76 MB respectively.

Figure 4. iops test data (parameter [3])

In terms of iops, momentus XT can reach about 116.

In general, it is similar to a common mechanical hard drive (such as WD's Scorpio blue
750 GB) compared with the momentus series with no built-in SSD, the performance is improved by about 60%, it is estimated that there are two reasons for the lack of Optimization for file systems and products.

Application

According to the test data of storgaemojo's Robert Harris on a 2009-year-old MacBook Pro
For the Leopard operating system, the speed of using a momentus XT hard disk is basically the same as that of a General hard disk, that is, about 45 seconds.
Air can be started in 15 to 20 seconds. Momentus
The XT hard drive performs very well. Although the speed of the first application startup is similar to that of the previous one, the second boot speed is greatly improved. For example, word is reduced from 12 seconds of the first time to less than 3 seconds of the second time, while final
Cut Pro is reduced from 45 seconds of the first time to 10 seconds of the second time.

 

Comparison

The following is my rough summary, and the data is not very accurate, but it should give you a general impression.

	SSD (SLC)	General mechanical hard drive	Hybrid
Read speed (per second)	200 + MB	70 MB	90 MB
Write speed (per second)	180 MB	70-MB	85 MB
Iops	1000 +	60	120
Market price (per GB)	60 yuan	1 RMB	2 RMB
Most suitable scenarios	OLTP	Save data	Daily Application

Table 1. Comparison Table

 

In terms of future predictions, Robert of storgaemojo
Harris is very optimistic about the mode. He thinks that the hybrid mode can provide good performance and hard disk capacity at a price close to the hard disk, and there is still much room for improvement in various aspects, particularly when Seagate began to produce hard disks in the hybrid mode on a large scale, he also felt that the Hard Disks Based on the hybrid mode were not yet mature enough to be used for raid. I personally prefer the hybrid mode because it fully inherits the traditional hard disk mode, so users can think of it as transparent, but in terms of performance, especially in terms of iops, the gap between iops and SSD is quite large, and in all aspects, it is the product itself. We still need to optimize the operating system, so I personally think the hybrid mode is good, but it is still far from the mainstream.

 

References:

1.  
   1. Seagate momentus XT
      GB hard drive performance test
      .
   2. Seagate
      Gets hybrid SSD/HDD right
      .
   3. Integrate readyboost Seagate to launch 2.5-inch momentus
      XT hybrid hard drive
      .