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This article provides an overview of the differences between the two interfaces SATA and SAS. It also offers information on SSDs. Moreover, it deals with the question why the use of SSDs leads to an increase in performance in BMD NTCS.
When it comes to running BMD NTCS, one of the most important factors is IOPS performance (input/output operations per second). How much traffic/how many operations can a medium (e. g. a hard disk or an SSD) process per second? However, we should bear in mind that there are other vital factors for good performance than data throughput (bandwidth).
MB/s and GB/s are important for:
IO/s are important for:
By now there are various interfaces which can be used to connect hard disks and SSDs. In this article we focus on SATA and SAS for HDDs. For SSDs interfaces NVMe (especially for servers) and M.2 (for consumers) can also be used.
Before addressing the differences of SATA and SAS interfaces, let us have a look at a speed comparison between an HDD and an SSD. For the use of database-oriented applications like BMD NTCS, critical factors include IOPS and latency of the respective media. Already, the advantage of an SSD over an HDD is readily apparent.
Test scenario | Consumer HDD | Consumer SSD |
4k Ran. Read IOPS | ~ 184 IOPS | ~ 65.000 IOPS |
4K Ran. Write IOPS | ~ 102 IOPS | ~ 94.000 IOPS |
4K Write Latency (Avg) | ~ 4.8ms | ~ 0.45ms |
| SATA | SAS |
Bandwidth | up to 6 Gb/s | up to 12 Gb/s |
Capacity | up to 8 TB | up to 1.8 TB |
Revolutions per minute | up to 7,200 | up to 15,000 |
Average access time | 7.6 – 12.0 ms | 2.9 – 4.0 ms |
Duplex mode | no | yes |
Dual porting | no | yes |
As for operating databases, only random I/O performance is relevant. When using one single SAS hard disk drive, random I/O performance is up to four times higher than when using a SATA drive (access time)! Moreover, a SAS hard disk drive can perform read and write operations at the same time (duplex mode)!
In addition, hard disk performance scales with the number of disks. In case of hard disk overload, speed often drops massively, even though processor, main memory and network are underutilized.
The number of disks is therefore crucial!
Capacity | Number of disks times capacity of the smallest single disk |
Speed | Very high, excellent write and read performance |
Probability of failure | Very high, failure of one disk causes loss of all data |
Costs | Very low, no capacity loss |
Minimum number of disks | 2 |
Application | Video editing, temporary storage |
Capacity | Half the number of disks times capacity of the smallest single disk |
Speed | High, read performance very good, write performance same as single disk |
Probability of failure | Low, failure of one disk does not cause data loss |
Costs | High, use of capacity reduced by 50% |
Minimum number of disks | 2 |
Application | Operating system, database, high I/O load |
Capacity | Half the number of disks times capacity of the smallest single disk |
Speed | Very high, read performance very good, write performance good |
Probability of failure | Low, failure of one disk does not cause data loss (security is 1 + x) |
Costs | High, use of capacity reduced by 50% |
Minimum number of disks | 4 |
Application | Databases, high I/O load |
Capacity | Number of disks minus 1 disk times capacity of the smallest single disk |
Speed | Average, read performance good, write performance moderate |
Probability of failure | Low, failure of one disk does not cause data loss |
Costs | Low, loss of only one disk |
Minimum number of disks | 3 |
Application | File server, test system, archiving, backup to disk |
Capacity | Number of disks minus 2 disks times capacity of the smallest single disk |
Speed | High but slower than RAID 10 |
Probability of failure | Low, failure of one disk does not cause data loss (security 1 + x) |
Costs | Average, loss of two disks |
Minimum number of disks | 6 |
Application | File server, database, high I/O load |
Capacity | Number of disks minus 2 disks times capacity of the smallest single disk |
Speed | Low, read performance good (~ RAID 5), write performance poor |
Probability of failure | Very low, failure of two disks does not cause data loss |
Costs | Average, loss of two disks |
Minimum number of disks | 4 |
Application | File server, test system, archiving, backup to disk |
Since SSDs are now available on both consumer and enterprise markets, let us have a look at the different features of this technology.
Almost all data that are processed in BMD NTCS are located in a database and, as previously mentioned, one of the most important factors for databases is I/O performance. Therefore, our application benefits from the use of SSDs. What do you have to consider when using SSDs?
There are differences in the architecture of SSDs and regular hard disks:
Advantages:
Disadvantages:
As is the case with hard disks, there are also differences between SSD models affecting mostly performance, lifespan, price and the area of application.
The memory that is used in an SSD has a particularly significant impact on price and endurance of the SSD. Contrary to hard disks, SSD memory can only be written to a certain amount of times before you cannot use the SSD anymore. SSDs that are used for normal (consumer) operation already have a lifespan of several years. This is mostly dependent on how much the SSD is used, though. Endurance is often specified using DWPD (Disk Writes Per Day) or TBW (Terabytes Written). As for SSD memory, the term “write cycles” is fairly common.
Below, you will find a list of the most common memory options that are used in SSDs depending on their respective area of application (PC, server, etc.).
TLC
Area of application | Consumer, mostly PCs, laptops, etc. |
Advantages/Disadvantages | Low price, short lifespan compared to eMLC and SLC, lower speed than MLC, SLC, etc. |
Write cycles | ~ 1000 |
MLC
Area of application | Consumer, mostly PCs, laptops, etc. |
Advantages/Disadvantages | More write cycles than TLC, often seen as a “pro” version of consumer SSDs |
Write cycles | ~ 3000 |
eMLC
Application | Enterprise, used for servers, workstations |
Advantages/Disadvantages | Fast memory, higher lifespan than MLC or TLC |
Write cycles | ~ 20,000-30,000 |
SLC
Application | Enterprise, mostly used for servers |
Advantages/Disadvantages | Very fast memory, very high price |
Write cycles | ~ 100,000 |
The most important factor for us is the difference in performance between SSD and regular hard disk. In the brief comparison between SSD and HDD performance below, two consumer products are compared. If we have a look at the values, we get an idea of the performance benefits that an SSD can offer. (Since it is not our objective to make recommendations for hard disks or SSDs, we do not name manufacturers. The test results have been provided by an external website.)
Test scenario | Consumer HDD | Consumer SSD |
4k Ran. Read IOPS | ~ 184 IOPS | ~ 65,000 IOPS |
4K Ran. Write IOPS | ~ 102 IOPS | ~ 94,000 IOPS |
4K Write Latency (Avg) | ~ 4.8ms | ~ 0.45ms |
Another test (different setting) compares the performance of hard disks (SAS) and the use of SSDs. Comparison: 14 x 10krpm SAS HDD (RAID5) vs. 6x SSD (SAS) RAID5.
Test scenario | 14x 10krpm HDD (SAS) RAID5 | 6x SSD (SAS) RAID5 |
8k Ran. Read IOPS | ~ 5,100 IOPS | ~ 118,000 IOPS |
8K Ran. Write IOPS | ~ 1,500 IOPS | ~ 31,000 IOPS |
8K Write Latency (Avg) | ~ 44.00ms | ~ 2.06ms |
In view of the reasons and results stated above, we can conclude that the use of or the change to SSDs can lead to an increase in performance when it comes to BMD NTCS, whether as a standalone or as a server installation.
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