Hi. In the LVM2 HOWTO, it says: (http://www.tldp.org/HOWTO/LVM-HOWTO/snapshotintro.html), "Full snapshot are automatically disabled" and: "If the snapshot size equals the origin size, it will never overflow.". But if one snapshot is created and an equal size is allocated to the snapshot, it still overflows (creates a volume with 32M, a snapshot with 32M, and fills the volume with zeros). Using more space, it doesn't overflow (same thing, but 64M for the snapshot). How much more space is needed to be alocated to the snapshot to ensure that it will never overflow? Thanks in advance, Guilherme. Script started on Tue 12 Feb 2008 02:11:11 PM BRST [root@localhost ~]# lvcreate -L 32M -n base_volume hf Logical volume "base_volume" created [root@localhost ~]# lvcreate -s -L 32M -n copy_volume /dev/hf/base_volume Logical volume "copy_volume" created [root@localhost ~]# lvdisplay |grep -A 13 "_volume" LV Name /dev/hf/base_volume VG Name hf LV UUID qPzWgG-ON3V-swUr-O0IP-I172-G3YV-GH431K LV Write Access read/write LV snapshot status source of /dev/hf/copy_volume [active] LV Status available # open 0 LV Size 32.00 MB -- LV Name /dev/hf/copy_volume VG Name hf LV UUID oGK0gG-o62D-Tu84-9CW0-rvPb-H7HX-bjUwk0 LV Write Access read/write LV snapshot status active destination for /dev/hf/base_volume LV Status available # open 0 LV Size 32.00 MB Current LE 1 COW-table size 32.00 MB COW-table LE 1 Allocated to snapshot 0.05% Snapshot chunk size 8.00 KB Segments 1 Allocation inherit Read ahead sectors 0 Block device 253:20 [root@localhost ~]# dd if=/dev/zero of=/dev/hf/copy_volume dd: writing to `/dev/hf/copy_volume': No space left on device 65537+0 records in 65536+0 records out 33554432 bytes (34 MB) copied, 8.01466 s, 4.2 MB/s [root@localhost ~]# lvresize -L 64M /dev/hf/copy_volume /dev/dm-20: read failed after 0 of 4096 at 0: Input/output error Extending logical volume copy_volume to 64.00 MB Logical volume copy_volume successfully resized [root@localhost ~]# lvdisplay |grep -A 13 "_volume" /dev/dm-20: read failed after 0 of 4096 at 0: Input/output error LV Name /dev/hf/base_volume VG Name hf LV UUID qPzWgG-ON3V-swUr-O0IP-I172-G3YV-GH431K LV Write Access read/write LV snapshot status source of /dev/hf/copy_volume [INACTIVE] LV Status available # open 0 LV Size 32.00 MB Current LE 1 Segments 1 Allocation inherit Read ahead sectors 0 Block device 253:18 -- LV Name /dev/hf/copy_volume VG Name hf LV UUID oGK0gG-o62D-Tu84-9CW0-rvPb-H7HX-bjUwk0 LV Write Access read/write LV snapshot status INACTIVE destination for /dev/hf/base_volume LV Status available # open 0 LV Size 32.00 MB Current LE 1 COW-table size 64.00 MB COW-table LE 2 Snapshot chunk size 8.00 KB Segments 1 Allocation inherit Read ahead sectors 0 Block device 253:20 [root@localhost ~]# lvremove /dev/hf/copy_volume /dev/dm-20: read failed after 0 of 4096 at 0: Input/output error Do you really want to remove active logical volume "copy_volume"? [y/n]: y Logical volume "copy_volume" successfully removed [root@localhost ~]# lvcreate -s -L 64M -n \ copy_volume /dev/hf/base_volume Logical volume "copy_volume" created [root@localhost ~]# lvdisplay |grep -A 13 "_volume" LV Name /dev/hf/base_volume VG Name hf LV UUID qPzWgG-ON3V-swUr-O0IP-I172-G3YV-GH431K LV Write Access read/write LV snapshot status source of /dev/hf/copy_volume [active] LV Status available # open 0 LV Size 32.00 MB Current LE 1 Segments 1 Allocation inherit Read ahead sectors 0 Block device 253:18 -- LV Name /dev/hf/copy_volume VG Name hf LV UUID LSUqQB-O2n4-8zmk-iL9n-2vDQ-qSsB-yOBDL1 LV Write Access read/write LV snapshot status active destination for /dev/hf/base_volume LV Status available # open 0 LV Size 32.00 MB Current LE 1 COW-table size 64.00 MB COW-table LE 2 Allocated to snapshot 0.02% Snapshot chunk size 8.00 KB Segments 1 Allocation inherit Read ahead sectors 0 Block device 253:20 [root@localhost ~]# dd if=/dev/zero of=/dev/hf/copy_volume dd: writing to `/dev/hf/copy_volume': No space left on device 65537+0 records in 65536+0 records out 33554432 bytes (34 MB) copied, 9.5375 s, 3.5 MB/s [root@localhost ~]# lvdisplay |grep -A 13 "_volume" LV Name /dev/hf/base_volume VG Name hf LV UUID qPzWgG-ON3V-swUr-O0IP-I172-G3YV-GH431K LV Write Access read/write LV snapshot status source of /dev/hf/copy_volume [active] LV Status available # open 0 LV Size 32.00 MB Current LE 1 Segments 1 Allocation inherit Read ahead sectors 0 Block device 253:18 --- Logical volume --- LV Name /dev/hf/F4_burn VG Name hf LV UUID Bj1VJS-1JUK-BA18-egFj-xOoY-qrbq-jbZFFY -- LV Name /dev/hf/copy_volume VG Name hf LV UUID LSUqQB-O2n4-8zmk-iL9n-2vDQ-qSsB-yOBDL1 LV Write Access read/write LV snapshot status active destination for /dev/hf/base_volume LV Status available # open 0 LV Size 32.00 MB Current LE 1 COW-table size 64.00 MB COW-table LE 2 Allocated to snapshot 50.12% Snapshot chunk size 8.00 KB Segments 1 Allocation inherit Read ahead sectors 0 Block device 253:20 [root@localhost ~]# exit Script done on Tue 12 Feb 2008 02:13:07 PM BRST [Gui@localhost:~]$ _______________________________________________ linux-lvm mailing list linux-lvm@redhat.com https://www.redhat.com/mailman/listinfo/linux-lvm read the LVM HOW-TO at http://tldp.org/HOWTO/LVM-HOWTO/
