UUID or universally unique identifier is a useful piece of information. It can be really handy sometimes when the name of the device or file systems are not consistent. Device UUID uniquely identifies the component in the system which is persistent across system reboots.
Device UUID
For CentOS/RHEL 5
# scsi_id -u -g -s /block/sda 35000c50032387713
For CentOS/RHEL 6
# scsi_id --whitelisted /dev/sdd 3600144f0da627ad70000503ad6ce0006
Or:
# udevadm info --query=all --path=/sys/block/sda P: /devices/pci0000:00/0000:00:01.0/0000:01:00.0/host0/target0:2:0/0:2:0:0/block/sda N: sda W: 99 S: block/8:0 S: disk/by-id/scsi-364403a78570b200018ac2cd20575ec04 S: disk/by-path/pci-0000:01:00.0-scsi-0:2:0:0 S: disk/by-id/wwn-0x64403a78570b200018ac2cd20575ec04 E: UDEV_LOG=3 E: DEVPATH=/devices/pci0000:00/0000:00:01.0/0000:01:00.0/host0/target0:2:0/0:2:0:0/block/sda E: MAJOR=8 E: MINOR=0 E: DEVNAME=/dev/sda E: DEVTYPE=disk E: SUBSYSTEM=block E: MPATH_SBIN_PATH=/sbin E: ID_SCSI=1 E: ID_VENDOR=LSI E: ID_VENDOR_ENC=LSI E: ID_MODEL=MRSASRoMB-4i E: ID_MODEL_ENC=MRSASRoMB-4i E: ID_REVISION=2.12 E: ID_TYPE=disk E: ID_SERIAL_RAW=364403a78570b200018ac2cd20575ec04 E: ID_SERIAL=364403a78570b200018ac2cd20575ec04 E: ID_SERIAL_SHORT=64403a78570b200018ac2cd20575ec04 E: ID_WWN=0x64403a78570b2000 E: ID_WWN_VENDOR_EXTENSION=0x18ac2cd20575ec04 E: ID_WWN_WITH_EXTENSION=0x64403a78570b200018ac2cd20575ec04 E: ID_SCSI_SERIAL=0004ec7505d22cac1800200b57783a40 E: ID_BUS=scsi E: ID_PATH=pci-0000:01:00.0-scsi-0:2:0:0 E: ID_PART_TABLE_TYPE=dos E: LVM_SBIN_PATH=/sbin E: DEVLINKS=/dev/block/8:0 /dev/disk/by-id/scsi-364403a78570b200018ac2cd20575ec04 /dev/disk/by-path/pci-0000:01:00.0-scsi-0:2:0:0 /dev/disk/by-id/wwn-0x64403a78570b200018ac2cd20575ec04
For multipath devices:
# multipath -ll -v 360080e500024a048000004044f3c64ee dm-0 SUN,LCSM100_F size=95G features='1 queue_if_no_path' hwhandler='1 rdac' wp=rw |-+- policy='round-robin 0' prio=6 status=active | `- 7:0:0:0 sdb 8:16 active ready running `-+- policy='round-robin 0' prio=1 status=enabled `- 8:0:0:0 sdk 8:160 active ghost running
Note: the device uuid is fixed value, the uuid of dm-mp device should be identical with the uuid of its paths. In most of situation could not be modified unless the device supports dynamic uuid feature.
Usage:
The device uuid often being used to persistent the device name or dm-mpath name, following example bind the wwid with name oraasm1 persistently.
multipath { wwid 36006048caf0b141598afa8e2875797a1 alias oraasm1 }
Note: the partition (such as sda1 sdb1) does not have uuid.
File system uuid
For CentOS/RHEL 5
# blkid /dev/sda1 /dev/sda1: LABEL="/boot1" UUID="ae298adb-1b94-42a0-9dc9-a121c7561a5b" TYPE="ext3" SEC_TYPE="ext2"
# /lib/udev/vol_id /dev/sda1 ID_FS_USAGE=filesystem ID_FS_TYPE=ext3 ID_FS_VERSION=1.0 ID_FS_UUID=ae298adb-1b94-42a0-9dc9-a121c7561a5b ID_FS_LABEL=/boot1 ID_FS_LABEL_SAFE=boot1
Note: the /dev/sdxx must be formated as file system.
Usage:
Could specify uuid in /etc/fstab to bind the device with mount directory persistently.
UUID=xxx-xxx-xxx-xxx /mount_dir ext3 defaults 1 2
Note: file system uuid will be changed after re-create file system.
LVM2 uuid
# pvs -v PV VG Fmt Attr PSize PFree DevSize PV UUID /dev/sda2 vg0 lvm2 a-- 48.81G 0 48.83G xCJzmN-oJmL-kMFl-JCrb-lfoH-movY-6x6K6O /dev/sda3 vg0 lvm2 a-- 48.81G 0 48.83G 9iXmmM-kKqV-OYDb-eSVN-ymCw-wwVk-uY6fXo
# lvs LV VG #Seg Attr LSize Maj Min KMaj KMin Origin Snap% Move Copy% Log Convert LV UUID lvroot vg0 3 -wi-ao 146.44G -1 -1 253 0 C0l0R2-KhH8-N7Nk-BhXn-MJhS-35dn-XXdL1B lvasmlib vg1 1 -wi-a- 4.88G -1 -1 253 6 5nlcKy-1kvs-l7qb-eIts-tEs6-E2JG-RisWDx
# vgs -v VG Attr Ext #PV #LV #SN VSize VFree VG UUID vg0 wz--n- 32.00M 3 1 0 146.44G 0 ereADB-2w9v-O2P9-58OS-RN9Q-t2pV-8wXpSc vg1 wz--n- 4.00M 3 3 0 139.71G 9.95G LczKdV-Nq82-lNrr-EmI1-cerd-numb-1qV6m4
Usage:
In some case need recover some pv device, use the –uuid and –restorefile arguments of the pvcreate command to restore the physical volume. The following command restores the physical volume label with the backuped metadata.
# pvcreate --uuid "0YnHNn-1COx-dohx-bwPf-aLyl-pO8F-f5PI5R" --restorefile /etc/lvm/archive/vg0_00000-1324010847.vg /dev/sda2 Physical volume "/dev/sda2" successfully created
Note: lvm2 uuid will be changed after re-create.