[kwlug-disc] iSCSI data integrity

R. Brent Clements rbclemen at gmail.com
Tue Apr 7 12:01:25 EDT 2009


I am not really qualified to answer these technical questions, but it
seems to me that since iSCSI is a data transport protocol, it only
really needs to be concerned with data integrity over the link, which
TCP/IP should suffice for.  One would assume that whatever physical
medium the LUN is on would provide its own mechanisms for ensuring
data integrity at the target end.

Brent

On Tue, Apr 7, 2009 at 9:52 AM,  <john at netdirect.ca> wrote:
> The question was asked in the meeting last night. Paraphrased it was "Does
> the iSCSI protocol provide for some level of data integrity, i.e. does it
> check sum?"
>
> The answer, according to RFC3720, is that by default it relies on the
> transport layer (TCP/IP in this case) to provide a CRC. It does go on to say
> that every initiator and target must support two options "No digest" and
> "CRC32C" digest for header and data digests.
>
> Documentation for the iscsitarget package also states that the default
> setting for HeaderDigest and DataDigest is "None".
>
> Typically, iSCSI is run over Ethernet. Both Ethernet and TCP provide CRC
> checks on the data packet. Ethernet's CRC is strong enough to ensure that
> only 1 out of 4 billion packets will have an undetectable error. (That's one
> bad 512B sector for 2 TB of data.) TCP's CRC is weaker. Since both would be
> in use the combination should be quite a but stronger.
>
> Does anyone know how that compares to the Reed-Solomon error detection used
> in hard disks?
>
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