Режимы iSCSI – Header digest, Data Digest

[MaxON]

Режимы iSCSI – Header digest, Data Digest –для чего нужны, какие возможности.

[exLH]

Performance of optimized software implementation
of the iSCSI protocol
The iSCSI protocol defines a 32-bit CRC digest on an iSCSI packet to detect the corruption of iSCSI PDU (protocol data unit) headers and/or data because a 16 bit checksum used by TCP to detect the corruption of a TCP packet was considered to be too weak for the requirements of storage on long distance data transfer [18]. These digests are called header digest and data digest respectively. When these digests are used, the iSCSI driver performs in a slightly different way.
1) The SCSI subsystem receives references to dirty pages from the VM system, and hands over them to the iSCSI driver.
2) The iSCSI driver associates these references with skbuffs for iSCSI packets by using sendpage interfaces.
3) If the header digest feature is enabled, the iSCSI driver computes a digest on an iSCSI PDU header.
4) If the data digest feature is enabled, the iSCSI driver computes a digest on an iSCSI PDU data, that is, the contents of dirty pages.
5) References are passed on to a network adapter driver and the contents of referred pages are transmitted by using DMA.