On Wednesday 25 June 2003 13:11, Ragnar Kjørstad wrote: > On Wed, Jun 25, 2003 at 11:46:34AM -0600, Andreas Dilger wrote: > > On Jun 25, 2003 18:00 +0100, Stuart Fox wrote: > > > I cant find information about the maximum volume group size in the > > > current 2.4 series kernel. > > > > > > Id like to be able to join 2 1.75Tb raid arrays into 1 3.5Tb array. > > > Is this possible? > > > > No, there is a limit of 2TB for all block devices in 2.4 kernels. With > > 2.5, there is a "large block device" configure option that lets you have > > larger block devices. There is apparently also a patch to support this > > on 2.4 kernels, but AFAIK it is not very widely used/tested. > > The question was regarding volum goups, not logical volums. > > So, correct me if I'm wrong, but I think the answer is yes, you will be > able to join 2 1.75 Tb volume groups into a single 3.5 Tb volum group, > if only an apropriate extent-size was set on VG-creation. The limitation for the size of a volume-group is a little obscure. The volume-group metadata (for LVM1 volume-groups - LVM2 format is probably different) stores the total number of PEs in the group as a 32-bit number. Thus, you are limited to 2^32 total extents. With a PE size of 4 MB, this is 2^54 bytes, or 16 exabytes (adjust accordingly for a different PE size). > However, each Logical Volum in the Volum-Group need to be smaller than 2 > TB. > > AFAIK the "large block device" feature in 2.5 does not enable > 2TB > logical volumes - it only fixes the general block-device layer, md and > the scsi-subsystem. At least that used to be the case - maybe someone > knows if it has changed? Again, the LVM1 format uses a 32-bit number to record the size (in sectors) of each LV. So the 2 TB limitation still exists. However, the metadata also records the number of extents allocated to the LV, so the tools *could* be written to ignore the lv-size field and always calculate based on the number of allocated extents. This would push the limit up to pe_size * 2^32 bytes, but would of course break backwards-compatibility with older tools (not sure if that really matters). -- Kevin Corry kevcorry@us.ibm.com http://evms.sourceforge.net/ _______________________________________________ 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/