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Re: [linux-lvm] LVM2 striping or md raid0

On Tue, 25 Sep 2007, Chris Cox wrote:

> This is merely my own opinion, but md was designed to be
> THE software raid mechanism.  So, my preference would be
> to establish a RAID md device and make that into a PV.

I prefer RAID1 integrated with LVM - it can handle mixed disk sizes 
with ease.  On a particular system with AIX LVM (where it has been integrated
for some time), We started with 3 512M disks, then added a 1G, then 2 4Gs, then
an 18G.  The filesystems were RAID1 at all times, and were expanded and PEs
moved between devices all with the filesystems mounted and active.
Linux LVM can do all this now, it is just a little kludgier at present.

With md, you have to arrange matching partition sizes by hand.  It *is*
possible, however, to move live/active md partitions between devices 
manually if you are careful (allocate partition on new device and add
as mirror, sync, set faulty and remove old partition).

Changing the partition table requires a reboot (or deactivating/unmounting all
partitions on the drive), so that limits what you can do live with md - unless
you have the foresight to divide your disks into roughly equal sized
partitions.  But that, of course, is what LVM does for you automatically.

	      Stuart D. Gathman <stuart bmsi com>
    Business Management Systems Inc.  Phone: 703 591-0911 Fax: 703 591-6154
"Confutatis maledictis, flammis acribus addictis" - background song for
a Microsoft sponsored "Where do you want to go from here?" commercial.

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