Since the availability of USB3 on the market, there has been a lot of guessing – and disappointments – regarding the performance of this new external attachment option. In this article I will try to clarify some facts that rule the speed of the various disk attachments.
Note1
Disk performance
It is important to understand what you can expect from your disk(s). Rotating disks will typically have Read/Write speeds between 60 and 100MB/sec, some are a bit faster. But this applies only if the blocks are rather large – 128KB or larger. If the blocks are small, e.g. 4KB as the Windows NT systems mostly use, the R/W speed will be significantly lower. 4KB is also the formatted blocksize on the current disk hardware.
If you want faster R/W speeds then you can choose an SSD. They provide speeds up to 350MB/sec for Reads and somewhat less for Writes.
The top dog in the disk speed race is a Revo drive which is configured as 4 way hardware Raid. They attach via PCI-E x4 and have R/W speeds around 500MB/sec and more (Example).
Attachment performance
USB2 can transfer data up to a maximum speed of 48MB/sec. That means that a fast disk or SSD cannot Read or Write at speeds at which it would be capable.
USB3 is a lot faster – it can transfer data at speeds up to 600MB/sec. However, there are no disks (rotating disks or SSDs) on the market at this time that can feed the attachment at that speed.
eSata is another option. It provides transfer capability up to 300MB/sec. That is ample for rotating disks and possibly a bit tight for top performing SSDs (if big blocksizes are used).
Firewire (IEEE 1394) is an external attachment method that comes in two versions – a 40MB/sec and an 80 MB/sec version.
PCI-E x4 is the attachment method for Revo drives. It can transfer data at speeds up to 1000MB/sec.
Measurements
I have measured USB2, USB3 and eSata on my systems. I use Atto because it seems to provide the most consistent results. But there are other measurement tools (e.g. HD Tune) that may provide slightly different numbers.
Test1 – here I use a 5400RPM disk running from USB2 and USB3
As you can see, USB3 is more than 4 times faster for large blocks and about 3 times faster for 4K blocks.
Test2 – here I use a 7200RPM disk attached to eSata
This is faster than USB3. The 4K times are twice as fast. But consider that this was a slightly faster disk. However, there have been several reports stating that eSata was faster than USB3 on other systems too.
Conclusion
Yes, USB3 provides fast data transfer speeds. But, there are no disks on the market right now that can exploit that capability. Rotating disks are probably maxed out with the 10.000RPM Raptors and SSDs are still too expensive for large amounts of data storage – and even the SSDs of today would not use the full USB3 capability.
I suppose we have to wait for the future developments in the disk technology to make full use of USB3. But then there is already Thunderbolt offered by Intel and Apple which provides PCI-E type performance for an external attachment. There is always the next step.
.
Note1
Note2
Disk performance
It is important to understand what you can expect from your disk(s). Rotating disks will typically have Read/Write speeds between 60 and 100MB/sec, some are a bit faster. But this applies only if the blocks are rather large – 128KB or larger. If the blocks are small, e.g. 4KB as the Windows NT systems mostly use, the R/W speed will be significantly lower. 4KB is also the formatted blocksize on the current disk hardware.
If you want faster R/W speeds then you can choose an SSD. They provide speeds up to 350MB/sec for Reads and somewhat less for Writes.
The top dog in the disk speed race is a Revo drive which is configured as 4 way hardware Raid. They attach via PCI-E x4 and have R/W speeds around 500MB/sec and more (Example).
Attachment performance
USB2 can transfer data up to a maximum speed of 48MB/sec. That means that a fast disk or SSD cannot Read or Write at speeds at which it would be capable.
USB3 is a lot faster – it can transfer data at speeds up to 600MB/sec. However, there are no disks (rotating disks or SSDs) on the market at this time that can feed the attachment at that speed.
eSata is another option. It provides transfer capability up to 300MB/sec. That is ample for rotating disks and possibly a bit tight for top performing SSDs (if big blocksizes are used).
Firewire (IEEE 1394) is an external attachment method that comes in two versions – a 40MB/sec and an 80 MB/sec version.
PCI-E x4 is the attachment method for Revo drives. It can transfer data at speeds up to 1000MB/sec.
Measurements
I have measured USB2, USB3 and eSata on my systems. I use Atto because it seems to provide the most consistent results. But there are other measurement tools (e.g. HD Tune) that may provide slightly different numbers.
Test1 – here I use a 5400RPM disk running from USB2 and USB3
As you can see, USB3 is more than 4 times faster for large blocks and about 3 times faster for 4K blocks.
Test2 – here I use a 7200RPM disk attached to eSata
This is faster than USB3. The 4K times are twice as fast. But consider that this was a slightly faster disk. However, there have been several reports stating that eSata was faster than USB3 on other systems too.
Conclusion
Yes, USB3 provides fast data transfer speeds. But, there are no disks on the market right now that can exploit that capability. Rotating disks are probably maxed out with the 10.000RPM Raptors and SSDs are still too expensive for large amounts of data storage – and even the SSDs of today would not use the full USB3 capability.
I suppose we have to wait for the future developments in the disk technology to make full use of USB3. But then there is already Thunderbolt offered by Intel and Apple which provides PCI-E type performance for an external attachment. There is always the next step.
.
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