SCSI and FC Standards Update
September 16, 2013, Storage Developer Conference, Santa Clara, CA—Fred Knight described the changes and updated in the main storage protocols. The standards process is fairly long and involved, so some of the changes are still under review.
The T10 committee is reviewing over 18,000 comments on SCSI commands, SCSI/ATA translation, SCSI express, and Serial Attach SCSI ( SAS). The drivers for the changes are the move from HDD to SSD and the accompanying increases in bandwidth, IOPS, and reduced latency. One additional issue is the flash media life cycles, which are stil under consideration.
New T10 features include atomic commands for all or none, interactions with traditional read/write commands, easier flash implementations, and scatter/gather commands. The new commands can simplify operations. For example, atomic operations can cancel all writes to a series of blocks if one LBA within the series has an error. The scatter write uses a range list to non-consecutive LBAs for the data. Gather read is a bi-directional command that uses the scatter range lists to read in data from the various blocks.
A simplified feature discovery uses a single command discovery to identify defined feature sets, base feature sets, drive management feature set, basic provisioning set, and other sets as needed. In addition, the command can obsolete old or unused features. The base feature set includes: inquiry, mode sense and select, report luns, report supported, opcodes/TMF, format unit, request sense, start/stop unit, read/write/verify/write same, and rad capacity. The set also eliminates duplicates.
The drive management feature set includes: log sense/select, format unit, read/write buffer, send diagnostics, reassign blocks, read defect data, sanitize, write long. Most of the features are for mainly for test purposes. The basic provisioning features get new functions for high availability, scatter/gather, atomic, and extended copy. Security through the Sanitize command overwrites the data, performs crypto scramble, block erase, and the command can be set for Whole logical unit. The Verify command has a new Verify Same option, and Time Limited Commands must complete or terminate. Other status information is accessed through Sense.
The new features also are looking at large scale configurations with billions of logical units. Report LUNS is an inventory discovery function for the conglomerate logical units or virtual volumes. The spec addresses administrative and subsidiary logical units and enables logical unit movement through binding/unbinding of data to the LUN.
The device crash dump has an in-band extraction of debug information that is either drive or initiator generated and uses the Read Buffer command. Returned information includes a vendor ID which indicates the company that can decode the VS information. The command uses common SCSI and ATA methods.
Banding in shingled magnetic recording (SMR) provides hints from storage to host and can operate with legacy use patterns for a slow response or intelligent use patterns for faster responses. the function also allows for demands from the storage to the host.
In the areas of transport, SAS 12 GB is complete with performance enhancements, and work is starting on the 24 GB standard. SCSI Express over PCIe is in the resolution phase as is direct connect storage in flash. iSCSI is being updated in iSER, MIB, and ipSec, and the fragmented sections are bringing all of the iSCSI functions into one place. New features for iSCSI include: Negotiated, priority field, and additional response information. The new iSCSI is fully back compatible with existing functions. new task management functions include Query Task, Query Task Set, I_T Nexus Reset, Query Async Event, and function Succeeded.
Fiber Channel gets a peer zoning where the target informs the SAN about zoning. Data speeds are increasing with 32GFC almost completed, and 128GFC to be implemented as 4X32 GFC. The specification allows for granularity at the 32 G level, inactivating the 128 GFC. When the 128 is active, the 32 GFC channels are inactive.
The FCoE VN2V point to point update operates on an Ethernet switch and fabric without any fibre channel switching elements. The SW6 committee has approved a distributed switch, and increased the domain and port counts. New management operations are also added.
New efforts are for energy efficient FC, with the copper version already completed through the IEEE and optical is ongoing. Also in the energy space, the energy star for switches standards are moving along.
