[rhn-users] LVM

[Greg Forte]

Wow, where to start ...

First of all, Travers: he's already got hardware raid, he said as much: 
"... went into the RAID BIOS ...".  It's built-in to the 6800 series.

Sead: your foremost problem is that you don't have enough disk space for 
any kind of meaningful redundancy if you need 100+ GB.  RAID0 isn't 
really RAID at all (unless you replace "redundant" with "risky") - RAID0 
stripes the data across N of N disks with no parity data, which means if 
one disk fails the whole system is gone.  Instantly.  It's basically 
JBOD with a performance boost due to multiplexing reads and writes.  To 
put it bluntly, no one in their right mind runs the OS off of a RAID0 
volume.

Beyond that, I'm surprised (impressed?) that the OS even still boots - 
after the conversion any data on the disks should be scrap.  Maybe the 
newer Dell RAID controllers are able to convert non-destructively.  I'll 
assume that's true, in which case the reason the OS doesn't see the 
difference is because you still need to change both the partition size 
(in this case, the logical volume extent size) and the filesystem 
itself.  In which case you COULD theoretically use lvextend to enlarge 
the LVM volume, and then resize2fs to grow the filesystem (assuming it's 
ext2/3, which it almost definitely is).  BUT, there's still the problem 
I mentioned above.

The first thing you need to do is fix the physical disk problem. 
Depending on how the machine is configured, this may be easy or hard.
A 6800 has 10 drive slots on the main storage backplane (the bays on the 
right), and if the two existing drives are on that backplane then it 
_should_ be a simple matter of buying a third 73GB disk, installing it, 
going into the RAID BIOS and converting again to RAID5 (assuming it can 
also do that conversion without trashing the disks - I'm guessing it can 
if it did RAID1 to RAID0), and then doing lvextend and resize2fs as 
described above (I know, you want more detail, but you need the disk 
first ;-)

BUT ... I'm gonna go out on a limb and guess that the machine was 
configured with the 1x2 secondary backplane in the peripheral bay area 
on the left.  If that's the case, then you're not going to be able to 
add a third disk in that area, and I don't think you can configure a 
raid with disk members on different backplanes - and even if you can, 
I'd guess the 10 bays in the main storage are all filled, or it wouldn't 
be configured with the extra backplane to begin with.  You'd have to 
check with Dell tech support about that, to be sure.  But assuming all 
of my guesses are right, the only option left is going to be to buy two 
larger disks and configure them for RAID1, just like the two 73's you've 
got now.  The other bad news in that situation is that you're probably 
going to have to reinstall from scratch - you could probably manage to 
image from the existing volume to the new one, but it's also almost 
surely going to end up being more effort (if you've never done that sort 
of thing before) than simply re-installing.

Good luck!  Once you do get the disk situation worked out, let us know 
and I (or someone else) can help you through the lvextend+resize2fs, if 
necessary.  I suspect you won't end up needing that, though.

-g

Travers Hogan wrote:
> It looks as if you have software raid 1. You cannot change this-you must rebuild your system. I would also suggest getting a hardware raid controller.
> rgds
> Trav
> 
> ________________________________
> 
> From: rhn-users-bounces at redhat.com on behalf of Sead Dzelil (Student)
> Sent: Sun 25/06/2006 03:10
> To: rhn-users at redhat.com
> Subject: [rhn-users] LVM
> 
> 
> 
> I am a system administrator with no experience with lvm. I have used
> fdisk in the past and I was very comfortable with that. I have a very
> important question. I have a Dell PowerEdge 6800 server that came with
> two 73GB hard drives in a RAID 1 configuration. The order was placed
> wrongly, because we need 100+ GB of storage. I went into the RAID BIOS
> and changed it from RAID 1 to RAID 0. Now the RAID BIOS display the
> logical volume with the full 146GB of storage.
> 
> The problem is that in the OS(RedHat Enterprise) nothing has changed.
> It still only sees the 73GB of storage. What can I do to get the
> system to see the whole 146GB? I need as detail info as possible
> because I have never used lvm before. Thank You in advance.
> 
> Sead
> 
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