Date: Wed, 8 Jul 2009 02:20:07 +0300 From: Dan Naumov <dan.naumov@gmail.com> To: Brooks Davis <brooks@freebsd.org> Cc: freebsd-stable@freebsd.org, freebsd-geom@freebsd.org Subject: glabel metadata protection (WAS: ZFS: drive replacement performance) Message-ID: <cf9b1ee00907071620i7a571be4w73aec90e97b3712a@mail.gmail.com>
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>> Not to derail this discussion, but can anyone explain if the actual >> glabel metadata is protected in any way? If I use glabel to label a >> disk and then create a pool using /dev/label/disklabel, won't ZFS >> eventually overwrite the glabel metadata in the last sector since the >> disk in it's entirety is given to the pool? Or is every filesystem >> used by FreeBSD (ufs, zfs, etc) hardcoded to ignore the last few >> sectors of any disk and/or partition and not write data to it to avoid >> such issues? > > Disks labeled with glabel lose their last sector to the label. =A0It is n= ot > accessible by ZFS. =A0Disks with bsdlabel partition tables are at risk du= e to > the brain dead decision to allow partitions to overlap the first sector, > but modern designs like glabel avoid this mistake. > > -- Brooks So what happens if I was to do the following (for the same of example): gpart create -s GPT /dev/ad1 glabel label -v disk01 /dev/ad1 gpart add -b 1 -s <ENTIREDISK> -t freebsd-zfs /dev/ad1 Does "gpart add" automatically somehow recognize that the last sector of <ENTIREDISK> contains the glabel and automatically re-adjusts this command to make the freebsd-zfs partition take "entiredisk minus last sector" ? I can understand the logic of metadata being protected if I do a: "gpart add -b 1 -s <ENTIREDISK> -t freebsd-zfs /dev/label/disk01" since gpart will have to go through the actual label first, but what actually happens if I issue a gpart directly to the /dev/device? - Sincerely, Dan Naumov
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