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CAM Target Layer

CAM Target Layer. Ken Merry Spectra Logic Corporation. What is CTL?. SCSI target emulation framework Can present a ramdisk , file, or block device as a SCSI target. LUNs visible through target-capable CAM SIMs . Only fully supported driver right now is isp(4).

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CAM Target Layer

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  1. CAM Target Layer Ken Merry Spectra Logic Corporation

  2. What is CTL? • SCSI target emulation framework • Can present a ramdisk, file, or block device as a SCSI target. • LUNs visible through target-capable CAM SIMs. Only fully supported driver right now is isp(4). • LUNs also visible through the internal CTL SIM.

  3. CTL History • Written for Copan Systems, starting in early 2003. • Originally written for Linux, has some similarities to CAM. Linux version had thousands of lines of CAM code included. • CTL originally meant “Copan Top Level”, and later “Copan Target Layer”. • Started shipping in 2005. • Ported to FreeBSD in 2008, when Copan ported their whole I/O stack to FreeBSD. • Currently ships in SGI’sArcFiniti and COPAN 400M/400T products.

  4. How CTL was Open Sourced • Copan’s assets bought by SGI in 2010. • Spectra Logic made a deal with SGI in 2010. • Spectra got the source to CTL under a BSD-style license, with the understanding that they would work to get it into FreeBSD. • CTL committed to FreeBSD/head and stable/9 in early 2012.

  5. CTL Features • Disk and processor device emulation • Tagged queuing • SCSI task attribute support (ordered, head of queue, simple tags) • SCSI implicit command ordering • Full task management support (abort, LUN reset, target reset, bus reset) • Multiple ports • Multiple initiators per port • Multiple LUNs • Multiple backend types

  6. CTL Features (continued) • Persistent reservations • Mode sense and select • All I/O is handled in-kernel, no userland context switches. • Basic High Availability support stubs. (Needs to be fleshed out.)

  7. CAM Structural Layout read, write, ioctl userland da(4) cd(4) sa(4) kernel CAM xpt isp(4) mps(4) SAN

  8. CTL Structural Layout ctladm read, write, ioctl userland da(4) cd(4) sa(4) ctl CAM periph CAM SIM IOCTL kernel CAM xpt CTL isp(4) mps(4) ctl2cam ramdisk block / file SAN

  9. Normal Target Command Path ctladm read, write, ioctl userland da(4) cd(4) sa(4) ctl CAM periph CAM SIM IOCTL kernel CAM xpt CTL isp(4) mps(4) ctl2cam ramdisk block / file SAN

  10. Internal Initiator Path ctladm read, write, ioctl userland da(4) cd(4) sa(4) ctl CAM periph CAM SIM IOCTL kernel CAM xpt CTL isp(4) mps(4) ctl2cam ramdisk block / file SAN

  11. Userland Path ctladm read, write, ioctl userland da(4) cd(4) sa(4) ctl CAM periph CAM SIM IOCTL kernel CAM xpt CTL isp(4) mps(4) ctl2cam ramdisk block / file SAN

  12. CTL Uses • Turn a FreeBSD box into an external RAID box. • CAM error injection testing: CTL used to test SCSI descriptor sense support for CAM. • SCSI testing without SCSI hardware • HBA bandwidth testing (using ramdisk backend) • Prototyping new OS features (e.g. trasz@FreeBSD.orggrowfs work)

  13. Demo

  14. To-Do List • Make CTL buildable as a module. • Use devstat(9) for statistics collection. • ZFS ARC backend for CTL. • Use CAM CCBs instead of ctl_io structure. • Full-featured High Availability support. • Allow sending status back with final data on reads. • Multi-thread CTL command processing. • Use busdma S/G list format. • Make data copy in the CTL SIM optional. • More driver support.

  15. Questions?

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