[KLUG Members] any experience with Debian Sarge & Dell 39160 SCSI controller?

[Mike Williams]

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>On Fri, 2005-09-02 at 08:27 -0400, adam at morrison-ind.com wrote:
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>>> I did a presentation on LVM & MD not too long ago.
>>> 
>>> What do you want to know?  I'm assuming the Debian installer lets you create
>>> logical volumes some kind of wizard?
>>> 
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>It appears the Debian installer supports setting up LVM on install. What
>I am trying to figure out and envision is how this works. 
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>1) So I setup the 3 drives in RAID 5. This gives me one "disk" to the
>partitioner that the LVM is setup on. Out of that I would setup
>a /boot /var /home and then I usually just leave the rest to /
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>2) So let's say that /home is getting full and I want to add another
>disk to it. Is it still going to be possible to add the disk to the raid
>array and somehow get that space into the LVM setup? All the docs I see
>have the examples just adding a new disk and mounting it then adding it
>to the LVM space. No one seems to talk about how it works with a RAID
>setup. 
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>I know I can set it up, what I don't know is if it is going to let me do
>what I want to do which is have a hot-swap disk in the machine and still
>be able to expand the filesystem as needed in the future. 
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>Thanks so much for the advice. 
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>Rick
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My advice would be to create swap and possibly /boot on the first few  
hundred megs of each drive, then make the RAID device (md0) from all the 
rest of the space.  Put one gigantic LVM partition on this new device.  
Create your LVM partitions for root, /var, /tmp, and whatever, but leave 
a third or so of the space unaccounted for.  Then when one of them fills 
up, you can add some of the remaining space.  Research your filesystem 
choice too, because the expand trick might only work if the filesystem 
is Reiser.

As far as buying a new disk and turning a 3-drive RAID 5 into a 4-drive 
RAID 5, I'm not sure that's possible.  It's not a trivial thing, to 
spread the data and parity to extra drives without losing anything.  
I've heard that 2-channel or better Compaq (no, I will NOT call them HP 
SmartArrays!) SCSI RAID controllers can do that stunt, but you're now 
talking about serious cash. 

Drives are cheap these days, even good ones.  Just buy more capacity 
than you expect to need and leave some free space in the LVM system.