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Re: [linux-lvm] Error setting up a mirrored lv

Laurenz, Dirk wrote:

i'm doing this:

hgest3301:~/LVM2.2.02.06 # lvcreate -m1 -n lvmirror -L 10G vgtest /dev/dm-55 /dev/dm-56
  Not enough PVs with free space available for parallel allocation.
  Consider --alloc anywhere if desperate.

what's wrong? Is there any documentation out there?
Why do we need three pvs? for a mirror?
Are there any other options?

As you noticed, you need a log partition. dm-mirror is a bit smarter then the basic MD raid1 in that it uses a log disk to keep track of write completions for synchronization. I've only recently got a kernel that supports modern mirror, but it looks like the log file sticks at a single extent even with a 20gb mirror (all my free space).

Is there a reason that the mirror is on a separate volume rather then a serialized metadata chunk at the end of each? Just for seektime performance reasons?

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