# File copying speed questions



## Rubnik (Jul 10, 2014)

Hello,
a few days ago while copying a file to my flash drive, and painfully watching the speed at 2Mb\s this subject kinda intrigued me (especially because my first thought was that something is wrong with my drive)

So anyway, say I'd like to copy a file from Drive A to B. From the little I know, copying speed should be determined by drive's A read speed, drive's B write speed, and the connection speed(usb 2\3, sata etc)?Essentially the copying speed being the slowest? Like in my case the write speed of my old USB drive?

Also why does the copy speed fluctuate? For example for my flash drive starts copying at about 6mb\s, and then for the most part stays at 2mb\s.Same happens with my SSD and HDD but thankfully at MUCH MUCH higher speeds


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## newtekie1 (Jul 10, 2014)

Speeds can fluctuate for a few reasons.  First, the transfer generally start off faster then settle down due to the file transfer using the cache of the drives and the burst speeds of the drives/connections.

Also, speeds can vary during a transfer because writing/reading different size files will affect speed.  So if you are reading/writing a bunch of very small files, the transfer speed will generally be a lot lower than if you are reading/writing one large file.


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## rtwjunkie (Jul 12, 2014)

Another thing, with flash memory, write speed has always been slower than read speed.  This persists to this day in most cases on SSD's.


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## newtekie1 (Jul 12, 2014)

rtwjunkie said:


> Another thing, with flash memory, write speed has always been slower than read speed.  This persists to this day in most cases on SSD's.


That is actually an issue with most HDDs as well.


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## fusionblu (Jul 12, 2014)

Rubnik said:


> Hello,
> a few days ago while copying a file to my flash drive, and painfully watching the speed at 2Mb\s this subject kinda intrigued me (especially because my first thought was that something is wrong with my drive)
> 
> So anyway, say I'd like to copy a file from Drive A to B. From the little I know, copying speed should be determined by drive's A read speed, drive's B write speed, and the connection speed(usb 2\3, sata etc)?Essentially the copying speed being the slowest? Like in my case the write speed of my old USB drive?
> ...



Quite easily USB flash storage pen drive speed can be influenced by type of HDD or SSD inside the machine (both the physical device itself, the controller they are connected to via motherboard in terms of hardware, firmware and drivers wise), the USB controller on the particular machine (which includes hardware, firmware and drivers) and lastly there is the performance of the USB pen drive itself.

Normally you would get good USB pen drive performance from machines with the latest hardware, updated with latest firmware and software, and when the machine is used with a new USB pen drive with good performance specifications.

As for speed fluctuations the first part of the process is often done with temporary burst speed and drops down to a sustained speed, and transfer speeds can vary with different types of files such as copying a single file (often fast), multiple files (normally take longer and can take longer than copying multiple files, which are collectively the same size, as a single file) or a compressed files with either a single or multiple files inside (normally faster than uncompressed files of the same set of files which were compress into the compressed archive file).


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## newconroer (Jul 13, 2014)

What confuses me is understanding which is the greater factor, the speed of the drive writing or the drive reading the copy. I've had scenarios where an SSD will write slower to an HDD, than the HDD writes to an SSD (of similar size files).

As for USB, never had a good experience with USB speeds, even on 3.0 controllers. The theoretical vs real world speeds of USB is shocking.


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## newtekie1 (Jul 13, 2014)

newconroer said:


> What confuses me is understanding which is the greater factor, the speed of the drive writing or the drive reading the copy. I've had scenarios where an SSD will write slower to an HDD, than the HDD writes to an SSD (of similar size files).
> 
> As for USB, never had a good experience with USB speeds, even on 3.0 controllers. The theoretical vs real world speeds of USB is shocking.



The slowest link in the chain will determine the transfer speed.

I'll give an example:

SSD Specs:
Read - 300MB/s
Write - 150MB/s

HDD Specs:
Read - 125MB/s
Write - 75MB/s

If you do a transfer from the SSD to the HDD, the read speed is capable of 300MB/s but the write speed is only capable of 75MB/s, so it will go at 75MB/s.  If you do a transfer from the HDD to the SSD, the read speed is capable of 125MB/s and the write speed is capable of 150MB/s, so it will go at 125MB/s.


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