In response to Mark Mielke <mark@xxxxxxxxxxxxxx>: > david@xxxxxxx wrote: > > On Wed, 26 Dec 2007, Mark Mielke wrote: > > > >> Florian Weimer wrote: > >>>> seek/read/calculate/seek/write since the drive moves on after the > >>>> read), when you read you must read _all_ drives in the set to check > >>>> the data integrity. > >>> I don't know of any RAID implementation that performs consistency > >>> checking on each read operation. 8-( > >> Dave had too much egg nog... :-) > >> Yep - checking consistency on read would eliminate the performance > >> benefits of RAID under any redundant configuration. > > except for raid0, raid is primarily a reliability benifit, any > > performance benifit is incidental, not the primary purpose. > > that said, I have heard of raid1 setups where it only reads off of one > > of the drives, but I have not heard of higher raid levels doing so. > What do you mean "heard of"? Which raid system do you know of that reads > all drives for RAID 1? I'm fairly sure that FreeBSD's GEOM does. Of course, it couldn't be doing consistency checking at that point. -- Bill Moran Collaborative Fusion Inc. http://people.collaborativefusion.com/~wmoran/ wmoran@xxxxxxxxxxxxxxxxxxxxxxx Phone: 412-422-3463x4023 ---------------------------(end of broadcast)--------------------------- TIP 3: Have you checked our extensive FAQ? http://www.postgresql.org/docs/faq
