媒體存儲技術(shù)-4存儲基礎(chǔ)iscsi-全文預(yù)覽
【正文】 ?Interactions/tradeoffs within/between levels ?Dynamic parameter adjustment C OMMUNICAITON UNIVERSITY of CHINA STORAGY LABORATORY iSCSI: Past, Present, Future Memory a Critical iSCSI Resource ?Initiator Paging to an iSCSI disk – VM system MUST NOT block for memory – Without care, standard TCP stack will block for memory (buffers and control structures) – Without care, iSCSI data path will block for memory ?Target memory starvation – May get multiple mands at once – Must hold memory until receipt acknowledged – Acknowledgement may be delayed indefinitely C OMMUNICAITON UNIVERSITY of CHINA STORAGY LABORATORY iSCSI: Past, Present, Future iSCSI: CPU Load ?CPU utilization is not negligible – Biggest percent from TCP/IP, not iSCSI or SCSI –Standard TOE offloading helps output – iSCSI HBA offloading helps input and output – Software iSCSI CRC is expensive for large PDUs C OMMUNICAITON UNIVERSITY of CHINA STORAGY LABORATORY iSCSI: Past, Present, Future CPU Overhead without HBA ?Interrupt rate – 1500 byte frame every 12 microsecs on 1 GE – 9000 byte frame every 5 microsecs on 10 GE ?Frequent cache flushing ?Extra copying – TOEs help mainly on output – Input requires intermediate TCP buffers or costly memory mapping C OMMUNICAITON UNIVERSITY of CHINA STORAGY LABORATORY iSCSI: Past, Present, Future iSER: iSCSI Extensions for RDMA ?Interface between iSCSI and RDMA ?iSER adds 12byte header to control PDUs ?Makes iSCSI independent of any protocol – RDMAP/DDP/MPA/TCP/IP – RDMAP/DDP/SCTP/IP – Infiniband – Others? (Myri?, Quadrics?) C OMMUNICAITON UNIVERSITY of CHINA STORAGY LABORATORY iSCSI: Past, Present, Future iSER: Concepts ?Target controls data flow – iSCSI read = target RDMA write – iSCSI write = target RDMA read ?4 new keys ?Old keys for digests, markers are irrelevant ?Handling of iSCSI PDUs – R2T, DataOut PDUs replaced by RDMA read – DataIn PDUs replaced by RDMA write – All other PDUs carried by RDMA send C OMMUNICAITON UNIVERSITY of CHINA STORAGY LABORATORY iSCSI: Past, Present, Future iSCSI/iSER Error Handling ?Guaranteed reliable, inorder deliver ?iSER error terminates connection! ?All iSCSI error recovery levels possible ?Level 1 reduced to almost nothing – Digest and sequence errors now impossible – PDU retransmission timeouts discouraged – SNACK must no longer be sent C OMMUNICAITON UNIVERSITY of CHINA STORAGY LABORATORY iSCSI: Past, Present, Future iSCSI: Sharing a Target Device ?Multiple hosts easily access mon target ?Efficient block transport directly to disk xNo notion of files, directories, data, or metadata xNo contention detection or resolution xNo allocation or management of blocks C OMMUNICAITON UNIVERSITY of CHINA STORAGY LABORATORY iSCSI: Past, Present, Future Objectbased Storage System ?Idea: pus
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