Date: Mon, 19 Sep 2005 15:56:25 +0700 From: Victor Sudakov <sudakov@sibptus.tomsk.ru> To: Danny Howard <dannyman@toldme.com> Cc: freebsd-geom@freebsd.org Subject: Re: Create a mirror on disk with valid data Message-ID: <20050919085625.GF73933@admin.sibptus.tomsk.ru> In-Reply-To: <20050917041700.GA46650@admin.sibptus.tomsk.ru> References: <20050916073012.GA31056@admin.sibptus.tomsk.ru> <20050916225527.GT11689@ratchet.nebcorp.com> <20050917041700.GA46650@admin.sibptus.tomsk.ru>
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Victor Sudakov wrote: > > > > I have only ever mirrored disks with data on them. Its a question of > > bootstrap - does the mirror comes first or does the data you are going > > to mirror come first? > > Suppose the disk has valuable data in the last sector and you are > going to create a mirror from this disk. What is going to happen when > the last sector is overwritten with the mirror metadata? Your data will > be lost, right? Suppose you need to access the last sector, access > will be denied, right? I have done some experimenting and found out the following. If you plan to put data onto a disk first, and convert the disk into a mirror later, the disk should be from the very beginning labelled so that the area for data is one sector smaller than disklabel suggests. If this condition is met, I believe converting a disk with data into a mirror is safe. -- Victor Sudakov, VAS4-RIPE, VAS47-RIPN
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