hesela.deviSCSI digest
An iSCSI digest is a negotiated check on a protocol data unit's header or data segment, conventionally using CRC32C for error detection.
HeaderDigest covers the basic and additional headers; DataDigest covers the data segment. Both include applicable padding, but an empty data segment has no data digest. The two keys are negotiated per connection and default to None. Negotiated digests apply in Full Feature Phase, not to Login Phase PDUs. CRC32C support does not establish that a digest was selected. [1]
A preference list such as CRC32C,None still allows no digest. A CRC32C-only offer has a different policy meaning. Check the negotiated connection settings rather than treating an offered list as an active setting. [2]
A CRC32C digest is not a message-authentication code or encryption. Application-layer error checks and packet security can have different protection endpoints. [3] Checking transport bytes therefore does not prove that a drive persisted a write.
Relations
Citations
- RFC 7143: digest coverage and negotiation, sections 11.2.3 and 13.1
- Open-iSCSI configuration at a65ce4b: digest preference lists
- RFC 3723: Application Layer CRC, section 3.6