On Wed, May 13, 2009 at 10:24 AM, Neil Brown <neilb@xxxxxxx> wrote: > On Wednesday May 13, sandeepksinha@xxxxxxxxx wrote: >> Hi, >> >> On Wed, May 13, 2009 at 10:01 AM, Neil Brown <neilb@xxxxxxx> wrote: >> > On Tuesday May 12, lrhorer@xxxxxxxxxxx wrote: >> >> >> >> But doesn't creating the array with the drive wipe the contents? If so, it >> >> doesn't seem to me this provides much redundancy. >> > >> > No. Creating an array does not wipe the contents. >> > It might cause a resync which will copy contents from one drive to the >> > other and I don't promise which one. >> > However if you: >> > >> Now, my question is that what if I create a RAID1 with 100 disks on each side. >> Do you mean to say that there will be unnecessary resync happening >> there as well, that too for unallocated/written data. > > I'm not sure what "100 disks on each side" means. > Do you mean a raid1 across 100 devices? i.e. 100 copies of each > block? > I meant we have two copies of 100 disks on each side of the mirror. Sorry, I am not very sure how md would handle it but say, I created two logical volumes of 100 disks and try to make a raid1 out of it. > In any case, md has no concept of unallocated/written data. Every > block is potentially meaningful and needs to be copied for resync. > So, while creation it is always guaranteed that a resync will always happen. I believe this can be avoided by just adding some flags. The user can specify its intention. > I have had thoughts about keeping track of which blocks have been used > so that 'TRIM' can be passed down. But it is a long way from being a > reality. > > >> >> If thats the case, we surely need to handle these two situations >> differently (1) which neil mentioned (2) the one I mentioned above. >> >> Remember I referring to the case of creation. >> >> > mdadm -C /dev/md0 --level 1 -n 2 /dev/foo missing >> > mdadm /dev/md0 --add /dev/bar >> > >> > then the contents on /dev/foo will not be changed (except for a few K >> > at the end for the metadata) and then all of foo will be copied to >> > bar. >> > >> >> Will the create happen at the first place? > > I don't understand this question, sorry. > Actually I could not understand, what did you mean by "missing" in the above line, which creates the array. > NeilBrown > -- Regards, Sandeep. “To learn is to change. Education is a process that changes the learner.” -- 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
