[linux-lvm] Snapshot Problem JFS

[David Sornig]

Heinz,
 
So to make a snapshot of the 1.4T LV which currently has a 400G of space being used by data I need to run the lvcreate command like this:
 
lvcreate -L1000M -s -n snap00 /dev/Volume00/LogVol00
 
I guess I thought the -L needed to be the same size as the current logical volume? 
 
Thanks,
 
David
 

	-----Original Message----- 
	From: Heinz J . Mauelshagen [mailto:mauelshagen at sistina.com] 
	Sent: Fri 6/20/2003 4:09 AM 
	To: linux-lvm at sistina.com 
	Cc: 
	Subject: Re: [linux-lvm] Snapshot Problem JFS
	
	

	On Thu, Jun 19, 2003 at 09:07:30PM -0500, David Sornig wrote:
	> I am running RedHat 9.0
	> Kernel 2.4.20-8
	> LVM Version 1.0.5+(22/07/2002)
	> 
	> I have a 1.4T LogVol with 400G of space being used on a JFS file system.
	> 
	> The LVM is working excellent.  However,  I cannot create a snapshot.  I run the following lvcreate command as per the man page and get the following error:
	> 
	> lvcreate --error "Cannot allocate memory"  creating VGDA for "/dev/Volume00/snap01" in kernel
	> 
	
	David,
	
	memory allocated to the snapshot needs free physical RAM.
	
	With 400GB and default snapshot extent size we're talking about ~1GB
	(using virtual memory for snapshot exception tables so that the table doesn't
	need to be in RAM completely any longer is a work item for LVM2).
	
	Do you really expect that much change to your 1.4TB LV during the lifetime of
	the snapshot ?
	If you use it for a backup, you might get along with a couple of GB allocated
	to the snapshot reducing exception table size drastically.
	
	
	> Not sure why this is happening.  I have read the list and maybe I just don't understand the problem.  These servers have 4 Gigs of RAM.
	> 
	> Regards,
	> 
	> David
	
	--
	
	Regards,
	Heinz    -- The LVM Guy --
	
	*** Software bugs are stupid.
	    Nevertheless it needs not so stupid people to solve them ***
	
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	Heinz Mauelshagen                                 Sistina Software Inc.
	Senior Consultant/Developer                       Am Sonnenhang 11
	                                                  56242 Marienrachdorf
	                                                  Germany
	Mauelshagen at Sistina.com                           +49 2626 141200
	                                                       FAX 924446
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