[Xen-users] Re: Safe partitioning for XEN?

[Kyler Laird <Kyler@xxxxxxxxxxxxxxx>]

Javier Guerra <javier@xxxxxxxxxxx> writes:

>AFAIK, GPT partitions can't be modified while online; that is, to repartiti=
>on=20
>your shared disk you'd have to stop any process that uses that disks.  Am I=
>=20
>right?

No, I regularly repartition on the fly.  That's the main reason that I
switched my latest Xen host to GPT.  It's a small single system at a
colo. provider.  It already had drives partitioned with msdos tables.  I
converted it to run Xen and I was going to leave the drives with msdos
partitioning but I got tired of rebooting everytime I made a change
(even when nothing was using the disk!).  I switched to GPT and it's no
longer a problem.

>if that's so, you could just as well use plain LVM.  it's safe to use on a=
>=20
>shared disk without any problem, just don't modify it while shared.  if you=
>=20
>want to change it, do a "vgchange <name> -an" on all nodes except one, chan=
>ge=20
>anything you want, and do a "vgscan; vgchange -ay" on the other nodes.

That's good to know.  That's not so different from running parted with
"set 1 boot off" to get the OS to re-read the GPT tables as I do now
when I make a change on a different machine.  Maybe I'll look at LVM
again.

Oh, one more little tidbit that I just learned but is probably obvious
to everyone else.  I started using GPT by simply running parted and
labeling a disk.  It just worked...but it didn't.  When I rebooted I
found that the OS didn't see all of the partitions.  I thought that this
was simply an ATA over Ethernet problem so I lived with it by using
"parted -s /dev/hdx set 1 boot off" as part of my startup.

On this simple system that I just created I'm not using ATA over Ethernet
but I still had this problem.  When I had first looked at advanced
partition selection in the kernel I saw this help text
        Say Y here if you would like to use hard disks under Linux which
        were partitioned under an operating system running on a different       
                                          architecture than your Linux system.
and decided I didn't need it.  After all, I wasn't using disks
partitioned on a different architecture.  Well, I finally decided to try
enabling this and I saw "EFI GUID Partition support".  I enabled that
and now my system recognizes the partitions without the help of parted.

--kyler


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