isp target mode bugs? (was Re: Missing sysctl options for isp driver)

[Trent Nelson]

> > > FreeBSD is the most up to date, but certainly has bugs in target mode. 

> > I, uh, I don't think I'm using target mode.  I've got four Xyratex RS- 
> > 1600-FC2 JBODs (16x146GB + 48x36GB) connected to two-but-soon-to-be-four
> > HP StorageWorks SAN Switch 2/16s.  Each FreeBSD box has a minimum of two
> > FC HBA ports; each HBA port goes to a different switch, and zoning config
> > on the switches controls which disks each hosts sees (although more on
> > this later).

> > So, uh, I think that constitutes fabric mode right?  The switch reports

> Target Mode is where the FreeBSD box can pretend to be a disk.  Yes,
> that's fabric.

    I disregarded target mode when I read your explanation, thinking it
    wasn't relevant to my environment.

    However, it dawned on me this morning how useful this could be.  Every
    box on my network has a minimum of two FC HBAs, and they're all capable
    of booting from an FC drive.  Other than the amd64 FreeBSD boxes, every-
    thing else is non-PC (SPARC, IA64, Power4+, PA-RISC etc).

    Having had an absolutely woeful experience with the Mylex FFx2 RAID 
    controller intended for the Xyratex enclosures, I've since decided to
    ditch it an leverage ZFS + JBOD instead.

    However, it's been bothering me a little bit that all the non-ZFS hosts
    wouldn't benefit from, er, ZFS.  I'd have to set up mirrored root volumes
    and all that crap to get a similar level of redundancy, but I'd be missing
    all the ZFS Good Stuff.

    I was planning on leveraging iSCSI (via zfs volumes), which would allow me
    to export ZFS-backed disks to non-ZFS hosts, but I'd really be only able
    to use those volumes for (non-important) data -- I couldn't boot off them
    nor have them as primary OS disks (limitation of old-ish hardware).

    As every box on the network has two FC HBAs, I found myself thinking this
    morning how useful it would be if I could present zfs volumes as disks to
    the SAN fabric, then zone/allocate them as if they were JBODs.

    ....ergo, target mode!
    
    Which makes your comment below all the more interesting:

> > > FreeBSD is the most up to date, but certainly has bugs in target mode. 

    What sort of bugs are we talking about? ;-)
    
    I'm pretty keen to explore this route after this morning's revelation.  I
    could boot all my AIX/HP-UX/etc boxes off ZFS-backed volumes; which means
    I could snapshot, clone, rollback, compress, dedup etc behind the scenes.
    Which would be absolutely bad-ass.

    What are your thoughts on this?  Viable option or are there fundamental,
    insurmountable technical issues that'll make my life miserable?


        Trent.

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