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Re: [linux-lvm] Flexible storga: LVM setup on top of mdadm sets. Good idea or not?



On Mon, Jul 23, 2007 at 12:43:17PM -0400, Stuart D. Gathman wrote:
On Mon, 23 Jul 2007, Luca Berra wrote:

On Sun, Jul 22, 2007 at 02:57:33PM -0400, Stuart D. Gathman wrote:
>The main drawback to md raid1 is that it always resynchronizes
>the *entire* partition when a disk goes offline temporarily.  I also
False. md uses bitmaps to avoid this.

I am using md on dozens of systems up through Centos-5.  If there are any
bitmaps, they don't work.  Or maybe they are a new feature not in kernel
2.6.18.  The only change I've noticed since RH7.3 is that sync speed is no
longer limited to 10K.  Or maybe I'm not looking at the right thing.
man mdadm
Bitmaps are a feature of md since mdadm-2.0 (kernel 2.6.13 or 2.6.14)

...

How would I see these bitmaps in action?

man mdadm
but basically
mdadm -G /dev/md?? -b internal

BTW, to upgrade a 7.2 system to Centos5, I plan to install on a disk
with matching partition sizes and replace boot drive.  Is there any
chance that md raid1 will sync from the old system overtop the new?
(Because the new wouild have lower sequence numbers?)  Or is there some
kind of UUID in the raid superblock to prevent this?  (Of course I plan
to change partition types away from RAID Auto just to be safe...)
unfortunately redhat insisted for a long time on using the in-kernel md
auto-detect, which iirc just ignores md uuid. i think this is still true
in redhat5.

changing partition type will prevent this
creating the new raid with a different minor will prevent this
or change the minor of the old raid.
... but we're getting offtopic.
if you have further questions post them on linux-raid.

L.


--
Luca Berra -- bluca comedia it
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