From mboxrd@z Thu Jan 1 00:00:00 1970 From: SandeepKsinha Subject: Re: Requesting replace mode for changing a disk Date: Wed, 13 May 2009 10:37:40 +0530 Message-ID: <37d33d830905122207pd676f00vac502f18d972dfae@mail.gmail.com> References: <4A060CBE.9090308@tmr.com> <20090513012112681.IEFQ19662@cdptpa-omta02.mail.rr.com> <18954.19719.172893.761454@notabene.brown> <37d33d830905122137l18f13c2aoec8e1cf67fdba2c0@mail.gmail.com> <18954.21141.982191.727975@notabene.brown> Mime-Version: 1.0 Content-Type: text/plain; charset=windows-1252 Content-Transfer-Encoding: QUOTED-PRINTABLE Return-path: In-Reply-To: <18954.21141.982191.727975@notabene.brown> Sender: linux-raid-owner@vger.kernel.org To: Neil Brown Cc: lrhorer@satx.rr.com, Linux RAID List-Id: linux-raid.ids On Wed, May 13, 2009 at 10:24 AM, Neil Brown wrote: > On Wednesday May 13, sandeepksinha@gmail.com wrote: >> Hi, >> >> On Wed, May 13, 2009 at 10:01 AM, Neil Brown wrote: >> > On Tuesday May 12, lrhorer@satx.rr.com wrote: >> >> >> >> But doesn't creating the array with the drive wipe the contents? = =A0If so, it >> >> doesn't seem to me this provides much redundancy. >> > >> > No. =A0Creating 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? =A0i.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. =A0Every > 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 use= d > so that 'TRIM' can be passed down. =A0But 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. >> >> > =A0 mdadm -C /dev/md0 --level 1 -n 2 /dev/foo missing >> > =A0 mdadm /dev/md0 --add /dev/bar >> > >> > then the contents on /dev/foo will not be changed (except for a fe= w 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 > --=20 Regards, Sandeep. =09 =93To learn is to change. Education is a process that changes the learn= er.=94 -- To unsubscribe from this list: send the line "unsubscribe linux-raid" i= n the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html