Reliability and Performance Comparison Between SSD and HDD

When buying a new computer, many users have to decide between purchasing a Hard Disk Drive (HDD) or Solid State Drive (SSD). There are many factors to take into account when making this decision. This article will highlight reliability and performance comparisons between HDDs and SSDs.

RELIABILITY
Moving Parts:
HDDs consist of one (or more) magnetically sensitive platters, an actuator arm with a read/write drive head on it for each platter, and a motor to spin the platters and move the arms. These moving parts in a HDD increases the risk of mechanical failures caused by electronic failure, sudden power failure, physical shock, wear/tear, or corrosion. Rough handling can also cause the moving parts to skip or sometimes fail.

On the other hand, SSDs do not require any moving parts. The technology in a SSD is a type of flash memory (3D V-NAND flash memory for Samsung 850 Pro). Floating gate transistors record a charge (or lack of a charge) to store data. Each time the user retrieves or updates data, the SSD controller will look at the address of the data requested and reads the charge status. Since SSDs accesses data completely electronically and do not require any moving parts, they are more durable to drop, shock, and vibration.

Fragmentation:
When HDDs access files, the drive head will note the positioning of the magnetic sections as it goes over the spinning platters. If the files being read are laid down in a sequential block, the HDD will be able to read the file quickly. However, when the HDD begins to fill up, files can be scattered across multiple sections. This results in fragmenting and will cause slower file read times. Periodic defragmentation is necessary to maintain optimum performance.
SSDs do not suffer from fragmentation, defragmentation will actually cause wear on the SSD by making additional writes to cells. Instead files can be written sporadically across the cells — and in fact are designed to do so — with little impact on read times, as each cell is accessed simultaneously. By being able to easily and simultaneously access cells, SSDs are able to read at a far faster speed than HDDs, regardless of fragmentation.

Susceptibility to Powerful Magnets:
HDDs use magnetic storage, which makes them susceptible to damage or data corruption when in close proximity with powerful magnets. Since SSDs do not require any magnetic parts to work, they are not vulnerable to powerful magnets.

Table 1.1, below lists out reliability specification comparisons between Samsung 850 Pro SSD and WD Black HDD. Since SSDs do not require moving parts, they do not have load/unload cycles or spindle start time specifications to take into consideration.

TABLE 1.1:

	Samsung 850 Pro SSD	WD Black HDD
MTBF	2,000,000 hours	1,000,00 hours
Load/Unload Cycles	N/A	300,000
Spindle Start Time, From Power-on to Drive Ready	N/A	4.0 sec avg
Spindle Start Time, From Power-on to Rotational Speed	N/A	2.0 sec avg
Shock (Non-operating)	1500G, 0.5ms	350G, 2ms
Temperature (Operating)	0 to 70 deg C	0 to 60 deg C
Temperature (Storage)	-45 to 85 deg C	-40 to 70 deg C

Table 1.1: Comparison between Samsung 850 Pro SSD and WD Black HDD specifications.

Performance
Table 1.2 compares HDTune, CrystalDiskMark, and Performance Test-DiskMark results between the same Samsung 850 Pro SSD and WD Black HDD. From the results, the SSD clearly outperforms the HDD by a wide margin, Performance Test ranks the Samsung 850 Pro SSD well above the world average (World Avg, Disk Mark: 2408) for storage, while the WD Black HDD ranks well below the world average.

TABLE 1.2:

	Samsung 850 Pro SSD	WD Black HDD
HD Tune - Benchmark	Min Read: 228.9 MB/s Max Read: 418.0 MB/s Avg Read: 409.9 MB/s	Min Read: 61.2 MB/s Max Read: 192.0 MB/s Avg Read: 143.5 MB/s
CrystalDiskMark	Seq Read: 527.4 MB/s Seq Write: 494.3 MB/s	Seq Read: 169.3 MB/s Seq Write: 84.59 MB/s
Performance Test - DiskMark Scores	Disk Mark: 5029 Disk Seq. Read: 516 Disk Random Seek+RW: 390 Disk Seq Write: 483	Disk Mark: 755 Disk Seq. Read: 123 Disk Random Seek+RW: 4 Disk Seq Write: 80

Table 1.2: Performance benchmarking between Samsung 850 Pro SSD and WD Black HDD. Using HDTune version 2.55, CrystalDiskMark2.2, and Performance Test version 9.