On Fri, Jun 20, 2003 at 12:29:15PM -0500, David Sornig wrote: > Heinz, > > Thank you for your help. Just want to make sure I understand perfectly what should happen. > > I have a Volume group with 4.2 T of space. In this Volume Group I have a Logical Volume called LogVol00 that is 1.4 T in size. Currently the LogVol has 400G of Data on it. In order to allow for approx 5% growth I need a snapshot of 420G or 1.470T. This is were I am confused. > If you want to allow for 5% changes on the original LV (1.4 TB), you want a snapshot size of 70 GB. Please remember: the snapshot only stores the changes to the original LV. > so I think I need the follwoing command. I am not in front of the system to test this so I am asking before I go forward since our live data is on this server. > > lvcreate - L 1.470T -s -n snap00 /dev/Volume00/LogVol00 lvcreate -L 70G -s -n snap00 /dev/Volume00/LogVol00 > > The reason I am trying to clarify is that I will be creating and destroying these using scripts and I do not want to have aproblem down the road without fully understanding. > You can check with "lvdisplay /dev/Volume00/snap00" hw much space is already used and if space isn't sufficient, you can grow it with lvextend. Regards, Heinz -- The LVM Guy -- > Thanks again for all of your help and sorry for being such a stickler for details. > > David > > -----Original Message----- > From: Heinz J . Mauelshagen [mailto:mauelshagen@sistina.com] > Sent: Fri 6/20/2003 9:50 AM > To: linux-lvm@sistina.com > Cc: > Subject: Re: Snapshot Problem JFS > > > > On Fri, Jun 20, 2003 at 06:43:40AM -0500, David Sornig wrote: > > 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 > > Yes, if you want to have a snapshot with a 1000MB exception store. > > > > > I guess I thought the -L needed to be the same size as the current logical volume? > > No, it doesn't need unless you have an update ratio of 100% to the original > during the lifetime of the snapshot. As a rule of thumb you can assume 5% > (which would be ~71g in your case) but that heavily depends on your > usage of the filesystem for obvious reasons. > > You can use lvdisplay on the snapshot to retrieve how much space is in use > and if it becomes full, you can lvextend it. > > Regards, > Heinz -- The LVM Guy -- > > > > > > Thanks, > > > > David > > > > > > -----Original Message----- > > From: Heinz J . Mauelshagen [mailto:mauelshagen@sistina.com] > > Sent: Fri 6/20/2003 4:09 AM > > To: linux-lvm@sistina.com > > Cc: > > Subject: Re: 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 -- > > _______________________________________________ > > linux-lvm mailing list > > linux-lvm@sistina.com > > http://lists.sistina.com/mailman/listinfo/linux-lvm > > read the LVM HOW-TO at http://tldp.org/HOWTO/LVM-HOWTO/ > > > > _______________________________________________ > linux-lvm mailing list > linux-lvm@sistina.com > http://lists.sistina.com/mailman/listinfo/linux-lvm > read the LVM HOW-TO at http://tldp.org/HOWTO/LVM-HOWTO/ > > *** Software bugs are stupid. Nevertheless it needs not so stupid people to solve them *** =-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=- Heinz Mauelshagen Sistina Software Inc. Senior Consultant/Developer Am Sonnenhang 11 56242 Marienrachdorf Germany Mauelshagen@Sistina.com +49 2626 141200 FAX 924446 =-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=- _______________________________________________ linux-lvm mailing list linux-lvm@sistina.com http://lists.sistina.com/mailman/listinfo/linux-lvm read the LVM HOW-TO at http://tldp.org/HOWTO/LVM-HOWTO/
