[linux-lvm] LVM + SAN Behavior

[gilles.massen at restena.lu]

Hello Dustin,

I feel somewhat relieved that I'm not the only one going to this sort of 
surprises :). I played around with our SAN, Linux, LVM, MD... only to 
discover quite some limitations in Linux.

Concerning the enlargement of partitions: from what I saw, the kernel does 
not re-read the partition table easily. Short of rebooting, this can be 
achieved by starting fdisk (which should reread the partition table on its 
own) and writing it to the disk. This makes the kernel reread the 
partition table IF there is no activity on the disk (i.e. no mounted 
partition or active volume-group). From that point you can then create a 
150GB partition, make it a PV and add it to your volume group. 

You could make the partition larger, but the only way I found was to 
delete the partition, and recreate it with another last sector (this is 
not for weak hearts) and even then I'm not sure that you can resize your 
PV easily.

Erm...sorry...I reread your posting: it seems you made the whole disk, not 
a partition, a PV? The you would need 'pvresize'. However when running it, 
it says: "command not implemented yet" (LVM2, latest release)

Gilles


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"Dustin Decker" <ddecker at kumc.edu>
Sent by: linux-lvm-bounces at redhat.com
19/01/2005 23:05
Please respond to LVM general discussion and development
 
        To:     <linux-lvm at redhat.com>
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        Subject:        [linux-lvm] LVM + SAN Behavior


Greetings/Salutations,
I have an interesting situation, and am hoping a few extra eyeballs may
help out.  The background:
 
SuSE Linux Enterprise Server 9.0 - fully patched
Root and swap partitions are "local", while we have a SAN which
provides additional storage over fiber.  For all intents and purposes,
the server sees this as a "local" disk as well.
 
Originally a single physical volume (/dev/sda which = 850GB SAN
allotment) was made part of a Logical Volume.  Now I am in need of
extending the logical volume to a full terabyte, which I expected to be
quite easy.  Our SAN administrator happily enlarged the volume we have
on the SAN by an additional 150GB, to equal a full terabyte.  The
server, even post reboot (M$ mentality, agreed), doesn't appear to know
about the additional 150GB.
 
What I am finding is that I cannot simply enlarge a physical partition.
 (Kinda felt like a "duh" moment.)  The real killer in this instance is
that our SAN supports expanding a SAN allotment, but not necessarily
reducing one.  Having asked my SAN admin to make this allotment larger,
I've pretty well made 150GB of disk space out there un-usable, as the
Linux system cannot (to my knowledge thus far) "see" it, and until such
time as the SAN allotment is deleted/recreated, the extra space is in
limbo.  (I.E. if I perform a pvcreate on /dev/sda, I expect now I would
get a full terabyte physical volume, but destroy the 850GB +/- 1% of
data currently there.)
 
I recognize that had the SAN provided us _another_ drive, vice
extending the size of what we had, I could have created a new PV and
extended our logical volume to include that.  Short term, we're hoping
an additional 1TB of space is available on the SAN so we can perform a
snapshot to it, destroy the current logical volume, and run with the
new, etc.
 
Is anyone aware of alternative methods I can use to reclaim this 150GB?
 Or perhaps you may have a better option for cleanup?  Granted, I could
just blow the whole thing away and restore from tape - but that would
take FOREVER.  Not an option on this system, it's already in
production.
 
Many thanks,
 
Dustin


--
Dustin Decker - Project Manager
Department of Information Resources
University of Kansas Medical Center
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Kansas City, KS 66160

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email: ddecker at kumc.edu

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