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$ get_block_name_prefix() {
> rbd info --format=json $1 | python3 -c "import sys, json; print(json.load(sys.stdin)['block_name_prefix'])"
> }
Short segments:
$ rbd create --size 12M img
$ DEV=$(sudo rbd map img)
$ xfs_io -d -c 'pwrite 5120 512' $DEV >/dev/null
$ xfs_io -d -c 'pwrite 12577280 512' $DEV >/dev/null
$ hexdump $DEV
0000000 0000 0000 0000 0000 0000 0000 0000 0000
*
0001400 cdcd cdcd cdcd cdcd cdcd cdcd cdcd cdcd
*
0001600 0000 0000 0000 0000 0000 0000 0000 0000
*
0bfea00 cdcd cdcd cdcd cdcd cdcd cdcd cdcd cdcd
*
0bfec00 0000 0000 0000 0000 0000 0000 0000 0000
*
0c00000
$ sudo rbd unmap $DEV
$ rbd rm --no-progress img
Short segment, ceph_msg_data_bio_cursor_init():
$ rbd create --size 12M img
$ DEV=$(sudo rbd map img)
$ xfs_io -d -c 'pwrite 0 512' $DEV >/dev/null
$ rados -p rbd stat $(get_block_name_prefix img).0000000000000000
.* size 512 (re)
$ xfs_io -d -c 'pread -b 2M 0 2M' $DEV >/dev/null
$ hexdump $DEV
0000000 cdcd cdcd cdcd cdcd cdcd cdcd cdcd cdcd
*
0000200 0000 0000 0000 0000 0000 0000 0000 0000
*
0c00000
$ sudo rbd unmap $DEV
$ rbd rm --no-progress img
Short segment, ceph_msg_data_bio_advance():
$ rbd create --size 12M img
$ DEV=$(sudo rbd map img)
$ xfs_io -d -c 'pwrite 0 1049088' $DEV >/dev/null
$ rados -p rbd stat $(get_block_name_prefix img).0000000000000000
.* size 1049088 (re)
$ xfs_io -d -c 'pread -b 2M 0 2M' $DEV >/dev/null
$ hexdump $DEV
0000000 cdcd cdcd cdcd cdcd cdcd cdcd cdcd cdcd
*
0100200 0000 0000 0000 0000 0000 0000 0000 0000
*
0c00000
$ sudo rbd unmap $DEV
$ rbd rm --no-progress img
Cloned bios (dm-snapshot.ko, based on generic/081):
$ rbd create --size 300M img
$ DEV=$(sudo rbd map img)
$ sudo vgcreate vg_img $DEV
Physical volume "/dev/rbd?" successfully created* (glob)
Volume group "vg_img" successfully created
$ sudo lvcreate -L 256M -n lv_img vg_img
Logical volume "lv_img" created.
$ udevadm settle
$ sudo mkfs.ext4 -q /dev/mapper/vg_img-lv_img
$ sudo lvcreate -L 4M --snapshot -n lv_snap vg_img/lv_img | grep created
Logical volume "lv_snap" created.
$ udevadm settle
$ sudo mount /dev/mapper/vg_img-lv_snap /mnt
$ sudo xfs_io -f -c 'pwrite 0 5M' /mnt/file1 >/dev/null
$ sudo umount /mnt
$ sudo vgremove -f vg_img
Logical volume "lv_snap" successfully removed
Logical volume "lv_img" successfully removed
Volume group "vg_img" successfully removed
$ sudo pvremove $DEV
Labels on physical volume "/dev/rbd?" successfully wiped* (glob)
$ sudo rbd unmap $DEV
$ rbd rm --no-progress img
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