gmirror, gpart and MBR vs GPT in the Handbook
jcigar at ulb.ac.be
Tue Dec 3 17:37:12 UTC 2013
On Tue, Dec 03, 2013 at 09:27:12AM -0700, Warren Block wrote:
> On Tue, 3 Dec 2013, Julien Cigar wrote:
> > On Mon, Dec 02, 2013 at 08:56:13AM -0700, Warren Block wrote:
> >> On Mon, 2 Dec 2013, Julien Cigar wrote:
> >>> If you want to use GPT with gmirror you may want to mirror each
> >>> partition instead of the whole disk.
> >>> For example on my box I have the following: https://dpaste.de/Rb3S
> >> There are a couple of potential problems with that. The big one is when
> >> a disk fails and is replaced. If you're not careful, the rebuild of all
> >> those mirrored partitions will start at the same time. Head contention
> >> will bring that to a near-standstill. It also puts a heavy load on the
> >> drive that still works. Hopefully it is not the same model and age as
> >> the one that failed, or its "warranty timer" may also be close to
> >> expiring.
> > That's true, I turned off autosynchronization of stale components to
> > avoid this kind of bad scenario ..
> >> A less-serious problem is that only the partitions are mirrored. That
> >> leaves out metadata like the partition tables and bootcode, but those
> >> typically do not change very often and might not be a problem. The
> >> admin has to remember to manually install such things on a new
> >> replacement disk, though.
> > It's just a matter of gpart backup / gpart restore, right ?
> That will get the partition tables but not the bootcode or PMBR. A
> failed disk could then leave a mirror which has all the data but is
ok, so I've to be sure that:
$> gpart bootcode -b /boot/pmbr -p gptboot -i 1 adaX
is executed for each disk involved in the mirror, right ..?
> At some point, we'll have to address the conflict between gmirror and
> GPT. ZFS mirrors can replace gmirror in some situations, but not all.
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