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I noticed in Windows 7 extracting rar to local hard drive is always significantly faster than to network storage (CIFS) or USB 3.0, even when the external storage has better sequential write performance than the local hard drive

I tested with winrar and 7zip and got similar results. Extracting to network storage (gigabit connection to FreeNAS CIFS) takes 3x longer, while cpu/memory/NIC usage are under 10%.

Normally I can paste files into network storage for 50MB/s+ (limited by local hard drive), but extracting gets like 2MB/s.

My guess is i/o latency really hurts performance in this type of application but I don't exactly know why. Does anyone have more insight into it? Thanks

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2 Answers 2

Normally whenever you extract a big file, when it has finished extracting you can then see it copying to the location you have extracted to from a temporary location. I imagine this is the case too with network drives. It most likely extracts to a temporary location on your local hard disk first and then copies to the network drive.

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This is the case for copy/paste extracting in WinRAR. I don't think extracting to destination actually involves this step tho. –  sdaffa23fdsf Aug 5 '13 at 20:41

This is because you are transmitting over to a shared drive using windows SMB rather than using FTP (File Transfer Protocol) which is meant for transferring large files. The big drawback to using SMB is that it encrypts traffic on both ends, meaning since you are putting files onto a shared drive, your data is extracted, encrypted, transmitted, then decrypted, potentially scanned for viruses, and finally written onto the shared drive. This causes significant drops in speed. The recommendation is to use SMB for smaller files, larger files should be transferred using FTP. A good solution would be to extract to local, then transfer using FileZilla or similar software.

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As I mentioned Samba can handle well over 50MB/s sequential write. I don't see how FTP can be a feasible alternative to Samba for local network share. –  sdaffa23fdsf Aug 5 '13 at 20:40
    
You don't mention samba at all in your question. In that case it may be the extraction process itself. Your comparison between pasting the file and extracting it are not comparable as they are entirely different processes. Pasting the file means that its entirety is available for transmission where as extracting it may very well mean that that only 2MB of data is available in any given second. –  Jason Bristol Aug 5 '13 at 22:13
    
Oh well I guess CIFS/SMB is interchangeable in many cases... And you even mentioned SMB in the answer.... When I say slower, it is kinda implied extracting to local hard drive is a lot faster.... –  sdaffa23fdsf Aug 6 '13 at 4:15
    
SMB stands for Service Message Block, it can also be referred to as CIFS or Common Internet File System (refer to my link). Extracting to local drive will always be a lot faster than extracting over a network. The real issue normally is the transfer protocol, but if you are using Samba then I am leaning a bit more towards the side of bandwidth issues. Your network card has to upload the data to your shared drive which will download it. Upload and download speeds are depend on your network setup and hardware. I would run a test on another computer and see if you get similar transfer speeds. –  Jason Bristol Aug 6 '13 at 12:18

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