The recurring question with respect to external hard drives circulates about the aspects, which determines the performance. Ideally, external hard disk designed with certain specifications should be independent of the external variants and deliver consistent performance. Had it been that simple and straight forward, our buyers easily would have understood the jargon used in the specifications and compare it with other products and finally buy the one which has the uniqueness applicable to their application. However, reality dishes out many variables that are highly interconnected. For example, consumers normally look for the external hard disk by understanding the positioning measurements rather than the transfer depth. Avoiding such ambiguities is possible if the buyer understands that the reading and writing process of an external hard disk actually depends on the manner in which the disk performs and at the same time about the external factors that either improves or reduces the performance level of an external hard drive. Therefore, in order to shed some light on the several aspects that need understanding prior to buying external hard drives, we have given a brief insight into the factors. We take you through this in the simplest way possible. Imagine that when an external hard drive connected to a system, two parameters come into the picture. One is the components and properties of the disk drive and secondly, the source to which it is connected and how well it is connected brings the difference. Therefore, we can simply say that EHD’s performance depends on the internals (of the disk itself) and the external (system and the interface) parameters.
The basic function of the external hard drive is to seek the correction location on the drive and secondly to either read or write the applicable data. Irrespective of the manufacturer, size or specifications all the drives follow this route. It is more like a mechanical process, wherein it physically transmits data from the platter surface to the cache (internal memory) and sends from this area to the interface. However, we have to understand that these two actions are completely different and hence depending on the design characteristics the speed varies. To simplify the lecture, we can define seeking the task of a drive to “positioning” and the data writing or reading task as “transfer”. Here, if you look closely, the positioning and the transfer performance is user-dependent. For instance, the hard disk performs numerous random accesses in the case where the user is running file server and the positioning execution should be rapid as it plays a vital role. However, data transfer performance is crucial if the user is carrying out multimedia re-work and the necessity to read or transfer the megabyte files as quickly as possible is important. The positioning and the transfer tasks of external hard drive, though appears simple, many minute characteristics influence the two basic actions of the drive. Firstly, the position performance is influenced by the seek time, latency, access time, track switch time, spindle speed and aerial density. The transfer performance is influenced by the Internal data transfer rate, spindle speed, and aerial density. We have tabulated the different characteristic design specifications and in what manner they influence.
Factors influencing Positioning performance
|Description||Definition||What to understand||Tips for the Buyer|
|Seek Time||Defines the time required for the heads( either read or write) to shift between the tracks||Many companies express seek time in 8 to 12ms range, although the time taken to seek from one track to another depends on the distance between them and is highly manufacturer dependent.||Never indulge too much in the seek time values and compare the disks based on this, because many instances the seek time is not required to determine the performance if you are reading chunkier data’s from the drive|
|Latency||Defines the waiting time required for the precise sector to arrive at the read or write head spot and is expressed in milliseconds||Latency depends on the disk-spinning rate. Faster the speeds quicker it will be for the sector to correctly locate and rotate under the heads and hence the latency would be lower||Buyers should look for the latency that is half the time it takes to make one complete rotation of the disk|
|Access Time||Defines the combination of seek time and latency and is expressed in millisecond||Positioning task depends on the disk ability to bring the head under the exact cylinder and simultaneously bring the correct sector beneath the located head so that it rotates underneath the heads||Access time is frequently is used in CD-ROM drives and has to be lower|
|Head Switch Time||Defines the time required to switch between heads inside a cylinder||The disk comprises of cylinders and each cylinder contains numerous tracks but in order to improve the speed instead of the head using one track at a time, the manufacturers design the drive to access all the tracks simultaneously by various heads and hence the head switch time comes to picture||Head switch time is often not indicated by manufacturers but we have to understand that drives having several platters switch between heads quite frequently|
|Track Switch Time||Track switch time is a mechanical process which defines the time taken for the head to move from one cylinder to the next one and is expressed in millisecond||Track switch time||Track switch time is important while processing heavier files|
Factors influencing Transfer performance
|Description||Definition||What to understand||Tips for the Buyer|
|Internal data transfer rate||The internal data transfer refers to the rate of data transfer within the drive||Ideally, the internal transfer rate could be produced of reading is for small sectors but in the real world the disk uses various heads to read a file||To measure the transfer rate one has to see the amount of data that is accessed over across a time spread. This value depends on the data density and disk spinning rate|
|Spindle Speed||Defines the positioning time and data transfer simultaneously||Drives with faster spindle speed have better performance and this is irrespective of the data streaming||Drives with 7200 RPM spindle speed delivers enhanced performance whereas 5,400 is regarded as slow|
|Aerial Density||Depends on the track density and bit density and this combined together influence the transfer and positioning rate||Track density determines the close package of the track and very close packing yields lesser seeking time.|
Bit density defines the arrangement of bits per track and when higher is the density the drive needs a lesser cylinder to keep 1MB file
|the latest drive consists of higher density per surface because of the technology manufacturers can accommodate the same capacity in a smaller surface|
External factors are those, which affect disk performance with respect to various connected components. Most importantly, the main area is the transfer of data between the interface and the system and hence slower speed of these components becomes a hindrance in the performance. Moreover, even for the same disk, the external factors operating on it vary depending on the type of environment. Here we simply use the term, interface or burst transfer rate to describe the speed at which things move between the disk and the system. Here, we have to understand the internal and external transfer rate, the latter one is much faster. In nonprofessional terms, the definition of the external transfer rate defines the speed of exchanging data between the computer’s memory and the cache (internal buffer) of the drive. Owing to the electronic nature of the data transfer operation, this takes quickly than the mechanical data transfer happening inside the disk. Popularly employed hard disk interfaces include SCSI and IDE/ATA. The latest interface consists of transfer rate very much higher than the internal rates and if it is not so, the buyer needs to understand that it is not been used to its fullest potential and needs updating. The recently used interface consists of a maximum 16.6MB/s transfer rate. Finally, the systems connected and shared using the interface dictates the performance. Especially in the case of SCSI which employs numerous devices unlike the IDE/ATA. However, employing four hard drives connected via SCSI in the server and the disk internal transfer rate is different, as it merely handles the multiple requests at ease.
Despite the efficient higher transfer rate integrated into the latest hard drives, one cannot isolate the hindrance that could possibly occur because of the slower main processing units available in some systems. Nevertheless, three main components of the system influence the performance of the hard disk. Firstly, the system processor or CPU speeds. Higher the CPU speed the better would be the data transfer. It is because the benchmark employed on the external hard drive requires the instructions processed on the CPU of the computer. Secondly, the motherboard, chipset, and the input and output bus play a role in determining the external transfer speed. The chipset oversees the bus operation and hence faster bus achieves better transfer speed. Thirdly, the system BIOS must support higher transfer speed and certain ones employ block mode that relatively enhances the system performance. To put it briefly, comparing drives gives partial conclusions because the drive’s performance is dependent on the system’s afore-said factors.
File System Factors
The logical structuring of the file system creates an effect on performance. Though they are independent on the disk, they create a similar effect on any external hard drive. The file structure and the cluster dimension, when used in DOS or windows application, have an impact on the speed. Despite the space wastage created by large clusters, they have the benefit of good performance because it creates lesser fragmentation and thereby saving more files in the block. An additional benefit is minimal overhead since the FAT is small. In addition to this, the file system with fragments degrades the performance. Unlike maintaining one chunkier file in the disk, when fragmented to pieces forces the disk to seek the information located on any track of the disk thereby creating a larger time to read. Finally, the disk partitioning effects because it directly points the cluster size. A smaller cluster refers to a larger partition and large clusters refer to smaller partition. Furthermore, depending on the zone bit recording the performance varies. For instance, the drive partitioned in three sections has the first section with better performance because it employs the external edge of the hard drive.
Finally, to conclude, though we have summarized the factors influencing the performance of your hard drive, it is a small summary and many finer details add momentum. Nevertheless, this article aims to assist you in choosing the best suitable external hard drive by understanding that besides the manufacture’s specifications there are parameters that could influence the actual performance of the drive and thereby you can buy the correct piece.