The fact that mirrors in a RAID1 set partially differ even on propper shutdown is caused by the ability to change dirty pages *while* they are being accessed (ie. by a mirroring driver). This has been a fact in Linux since ever and is expected behaviour with eg. filesystems, direct IO and memory mapped files. Mind you that this is a block level inconsistency only, because the fs/application will always write before it'll read the blocks in question unless it is not well-behanved. An example for a filesystem causing this is a file write followed by a file truncation. Regards, Heinz -- The LVM Guy -- On Thu, Mar 02, 2006 at 02:48:25PM +0100, Mario 'BitKoenig' Holbe wrote: > Kasper Dupont <48755289462761382922@xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx> wrote: > > A bit too aggressive it seems. How can it end up being marked > > clean when the two mirrors differ? > > Do you have write-cache enabled on the mirrors? > > Sometimes I have differences between RAID1 mirrors in 2.4, too. Even with > clean shutdown or reboot sequences. However, in my case, it turns out > that this always affects areas which are "free" on the filesystem layer. > This assumption is especially feeded by > a) the fact that the content of at least one of these differing areas is > typically zeroed and > b) that I have md5sums of all my files which don't show up any > differences when I either copy the non-zero content over the zeros or the > other way around. > Especially I have never experienced such "normal" differences on my swap > RAID1 mirrors. Until now I thought this would have to do with kernel 2.4 > and block-device-specific dirty-page-flushing and missing write-barriers > and things like that which lead to blocks used for a short time only get > flushed to the one mirror but not to the other (and then, since they are > freed again, the flush to the other mirror will never happen, since the > associated pages are just not dirty anymore). > However, I thought - at least until now ;) - this would change with 2.6, > since there md has more control over the block-devices it uses. > > > regards > Mario > -- > The question of whether a computer can think is no more interesting than > the question of whether a submarine can swim. -- E. W. Dijkstra > > - > To unsubscribe from this list: send the line "unsubscribe linux-raid" in > the body of a message to majordomo@xxxxxxxxxxxxxxx > More majordomo info at http://vger.kernel.org/majordomo-info.html =-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=- Heinz Mauelshagen Red Hat GmbH Consulting Development Engineer Am Sonnenhang 11 Cluster and Storage Development 56242 Marienrachdorf Germany Mauelshagen@xxxxxxxxxx +49 2626 141200 FAX 924446 =-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=- - To unsubscribe from this list: send the line "unsubscribe linux-raid" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
