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I'm used to consider that USB transfers are safe for data, that is USB does not add level of unreliability to data storage.

However, I read that USB is not always a good choice for data transfer concerning its reliability. For instance, It seems that using USB disk in a RAID is not a good idea.

I would like to know if the risk of data loss is specific to the way RAID works, or is intrinsic to every USB transfer.

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  • 1
    IMO this question is better suited for Information Security. Sep 25, 2020 at 6:08
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    USB is a communications protocol. What's relatively safe or unsafe depends more on the storage media, which you didn't specify. Sep 25, 2020 at 6:15
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    Could you please specify more details on what RAID and what drives are you planning to use?
    – Strepsils
    Sep 25, 2020 at 7:37
  • @GeraldSchneider Here I'm not taking about securely transfering data by preserving its confidentiality, but rather i'ma talking about preserving its integrity
    – abitbol
    Sep 25, 2020 at 10:41
  • @MichaelHampton The question is not about the storage media but on reliability of link between computer and this media. I could put it differently : given a storage media, considering only integrity of data, would it be strictly better to use sata connexion or putting the storage media in a USB dock is as reliable as sata connection.
    – abitbol
    Sep 25, 2020 at 10:49

1 Answer 1

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USB data path is protected by checksums on the both sides.

https://www.beyondlogic.org/usbnutshell/usb3.shtml

(Watch out CRC field within USB data packet structure)

This is the quote from the original USB specification:

8.3.5 Cyclic Redundancy Checks

On the both ends of USB wire, hardwares (PIC USB peripheral and host controller on PC) check CRC to detect packet error (#1). For Control, Interrupt and Bulk transaction, the occurance of error is shared by both ends by absence (not in time) of handshake (ACK) packet at the transaction (#2). And then, host controller retries the transaction, two times more (error correction). At the third error, host controller reports transfer error to the PC driver (#3). In Isoc transaction, error is detected, but the error handling is upto application over the USB protocol.

You can download full USB 2.0 spec for your reference here:

https://www.usb.org/document-library/usb-20-specification

Hope this helped!

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    Thank you for the answer. Thus in this case, why OpenMediaVault refuse to use USB-connected disks to create RAID array?
    – abitbol
    Sep 26, 2020 at 5:01
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    My guess is: Because external disks can be unplugged any moment losing WBC. Either way - ask them :) Sep 26, 2020 at 13:19

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