Re: consistency detect

[Ming Zhang <mingz@ele.uri.edu>]

On Mon, 2004-10-11 at 20:13, Neil Brown wrote:
> On Monday October 11, mingz@ele.uri.edu wrote:
> > :) thanks a lot. so now i know what policy raid1 use. so raid1 will
> > randomly choose first drive and sync among all drives. so here comes to
> > another question. after a power loss and reboot, raid1 knows that there
> > are something wrong and potentially out of sync between two drives. will
> > it try to check and make sure two drives are in sync or it just leave
> > two drives there with potential unmatched blocks.
> > 
> > for example, before reboot, a write to location A happen in progress.
> > then after reboot. raid1 has no idea on previous write information. it
> > just knows something might happened and two drives are possible to be
> > out of sync. will it check whole drive to do a resync?
> > 
> 
> Yes.  It copies all of these first drive onto all of the other drives.
a full copy? then if u have 100GB on first disk and you have to copy
that much? with background reconstruction, this can take a long time. i
never realized the overhead is this high. so i guess if system provide u
a piece of nvram, u can do much better. :P


> 
> NeilBrown
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