Raid5 LVM - tips on OS change/upgrade.

Adam Hawes adam at
Wed Feb 4 13:35:32 CST 2009

>> It sounds like you're doing some fancy stuff with a hardware RAID
>> controller which will simply give you a single disk to detect.
> Is this the same if each raid controller presents two drives to the OS which
> are then LVM'd?

Yes, it is.  Linux will simply see two drives and each with have
RAID/LVM config sectors on them.  The kernel will be able to put the
LVM back together from there.

> One more question:
> Is there is no need to vgexport either LVM before the re-install?

That isn't a bad idea - it'll make the volumes inactive so the
installer won't try and load them and bollocks them for you.  You can
reactivate them one by one when you have the new system built.

> All things above being good, our newly formed plan is;
> -Shutdown & remove hw raid controllers (our paranoia in action!)

Good plan - if the HW RAID controllers are gone then a (possibly)
crappy install error (usually between the keyboard and chair) can't
format your 3TB of disks and then install Debian on the largest

> -Swap current md0 drives for new hdds (to at least keep the old install
> intact)

Also good, in case it fails.  Just pop the old disks in and reactivate
the volumes and boot back to a working system.  Minimal downtime.

> -Install w raid1 debian etch and check all booting etc.

Good to do.  Configure the box as far as you can without the 3TB of
data attached.  Less chance you'll hose your data while logged in as

> -Re-introduce one raid controller (w smaller lvm on it ~ 1Tb) and test
> mounting - we can afford to loose this bit of data for a short period as its
> only an offsite backup)

Good data to test on.  I don't think you're going to see any problems.
 Unless you uncover a massive bug in the kernel or an error between
the keyboard and chair slips in you will be fine.  I've moved LVM
volumes on USB disks between machines with different distros and they
have survived just fine.

> -if all ok, shutdown and add other controller and mount
> -pray to the gods of linux then find Adam and buy him a beer (or something
> else if he doesnt drink beer)

beer == good

> Sound ok?

Doesn't sound like you need my help - your plan's only possibly fault
is human involvement.



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