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

[Luca Berra]

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 at comedia.it
        Communication Media & Services S.r.l.
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