Re: Informix vs. AIX Mirroring

In article <52p08p$68c@cssun.mathcs.emory.edu>, Jack Parker <jparker@boi.hp.com> writes > >I disagree. Filesystem damage can 'take down' a primary drive. Since >it is generally a raw device - hte Unix mirroring will never notice a need >to switch over where the Informix mirroring will. Where we have used >Informix mirroring we have been very happy with it. Where we have not >we have had this sort of problem. Surely filesystem damage will occurs because of 3 possible things:- a) A bug in Informix - which would affect both mirrors together. b) A power fail/suddenly loss power e.g. cleaner knocks the power lead out (has happen!!), Which again would leave the mirrors inconsistent. But you'd be lucky if either was consistent in this case. c) Hardware failure/disk error. someother reason why the disk can not be written to. This should be caught by AIX mirroring - that is what it is for. d) Failure to swtich one of the mirrored disks. In which case Informix would flag the mirror as down (MD/PD) which is hard to recover from basically a level 0 restore/ dbspace restore is required to bring either the mirror or primary chunk(s) back online. UNIX mirroring would mark the primary/mirror as failed. THEN YOU CAN BRING IT BACK i.e. resync the mirror. It's easier to restart mirroring after a drive failure under UNIX. (I'd forgetten this bit in my last post). To do an upgrade we once 'broke' a mirror to get a couple of gig of space and then restarting mirroring. It caught back up and then was ok. Admittedly this was on a Pyramid Wouldn't AIX be similar. Why else would a mirror fail and UNIX not detect it? -- David Williams