Date: Sun, 5 Feb 95 13:33:41 MST From: terry@cs.weber.edu (Terry Lambert) To: rjs@clark.net (Ron Steele) Cc: freebsd-questions@freefall.cdrom.com Subject: Re: Disk Mirrors Message-ID: <9502052033.AA02973@cs.weber.edu> In-Reply-To: <Pine.SOL.3.91.950203204212.24479A-100000@explorer> from "Ron Steele" at Feb 3, 95 09:07:08 pm
next in thread | previous in thread | raw e-mail | index | archive | help
> So, I would be interested in developing some sort of mirroring/logical > volume capability for FreeBSD. I feel that this would lend a lot of credit > to FreeBSD as a "commercial" product, and perhaps make it a more > acceptable replacement for commercial Unix systems to people > that may be reluctant to use a freeware product. > > I am an experienced C/Unix person, but have never gotten my feet wet > in the kernel, so I would need some mentoring. Still I think I could > pull this off with a little help. > > If anyone else is interested in pursuing this please email me. Some > words of encouragement from an experienced file system person would be > especially welcome. A "correct" implementation would require file system changes to insure cross volume staggered synchronization and two drive recovery using fsck to pick "more correct" information for best recovery. A quick and dirty implementation would require the minimum work, that of abstracting geometry and offset information for non-identical drives to provide the lessor of two sector extents in the case that the disks are not identical. It would also require "perfect media" -- or pseudo-perfect. For other than SCSI, this means getting BAD144 working reliably. If you didn't do this, indexing would be a nightmare, as would identically selecting inodes and disk blocks for use without some kind of master/slave relationship between the drives (symmetry is the key). This probaly means VM changes for dirty page handling. I would suggest checking out the papers on Zebra and other high availability work in the past Proceedings of Usenix (ftp.sage.usenix.org). Not that I recommend Zebra. Terry Lambert terry@cs.weber.edu --- Any opinions in this posting are my own and not those of my present or previous employers.
Want to link to this message? Use this URL: <https://mail-archive.FreeBSD.org/cgi/mid.cgi?9502052033.AA02973>