Seagate announced their split actuator SAS drive, which will probably require some kernel changes for full support. It's targeted at cloud provider JBODs and RAID.
Here are some of the drive's architectural points. Since the two LUNs share many common components (e.g. spindle) Seagate allocated some SCSI operations to be LUN specific and some to affect the entire device, that is, both LUNs. 1. Two LUNs, 0 & 1, each with independent lba space, and each connected to an independent read channel, actuator, and set of heads. 2. Each actuator addresses 1/2 of the media - no media is shared across the actuators. They seek independently. 3. One World Wide Name (WWN) is assigned to the port for device address. Each Logical Unit has a separate World Wide Name for identification in VPD page. 4. 128 deep command queue, shared across both LUNs 5. Each LUN can pull commands from the queue independently, so they can implement their own sorting and optimization. 6. Ordered tag attribute causes the command to be ordered across both Logical Units 7. Head of Queue attribute causes the command to be ordered with respect to a single Logical Unit 8. Mode pages are device-based (shared across both Logical Units) 9. Log pages are device-based. 10. Inquiry VPD pages (with minor exceptions) are device based. 11. Device health features (SMART, etc) are device based Seagate wants the multi-actuator design to integrate into the stack as painlessly as possible.The interface design is still in the early stages, so I am gathering requirements and recommendations, and also providing any information necessary to help scope integrating a multi-LUN device into the MQ stack. So, I am soliciting any pertinent feedback including: 1. Painful incompatibilities between the Seagate proposal and current MQ architecture 2. Linux changes needed 3. Drive interface changes needed 4. Anything else I may have overlooked Please feel free to send any questions or comments. Tim Walker Product Design Systems Engineering, Seagate Technology (303) 775-3770
