last modified by Nitin Yewale on 01/10/12 - 11:54
How do I create persistent device names for attached SCSI devices that will not be changed on reboot or when new devices are added or existing devices are removed?
Red Hat Enterprise Linux (RHEL) 6
Red Hat Enterprise Linux 5.3 and later
- Red Hat Enterprise Linux 4.7 and later
The udev rules supplied with Red Hat Enterprise Linux 6, 5.3 and later, and 4.7 and later can create persistent device names for SCSI devices. These names are actually persistently-named symbolic links that appear in /dev/disk/by-id (for disk devices) and /dev/tape/by-id (for tape and media changer devices). These symbolic links, which use persistent device attributes (like serial numbers), do not change when devices are added or removed from the system (which causes reordering of the /dev/nst* devices, for example).
Use of these persistently-named symbolic links is highly desirable in, for instance, the configuration of backup software (which is commonly a static definition that binds a backup software device name to an operating system-level device file name).
Note: that these persistently-named symbolic links are created in addition to the default device file names in /dev (for example, /dev/nst0).
For Red Hat Enterprise Linux 4 only
By default, a Red Hat Enterprise Linux 4.7 system will not create these persistently-named symbolic links in /dev/[disk|tape]/by-id. For the persistently-named symbolic links to be created, /etc/scsi_id.config must be modified as follows:
options=-g -u
Following this modification, the system should be rebooted or run command start_udev to enable creation of the persistently-named symbolic links.
Comments
Reference Links - RHEL6
- Persistent Naming section in the Red Hat Enterprise Linux 6 Storage Administration Guide.
- Configuring persistent storage in Red Hat Enterprise Linux 6 section in the Red Hat Enterprise Linux 6 Virtualization Guide.
Reference Links - RHEL5
Persistent Naming chapter in the Red Hat Enterprise Linux 5 Online Storage Reconfiguration Guide.
Configuring persistent storage in Red Hat Enterprise Linux 5 section in the Red Hat Enterprise Linux 5 Virtualization Guide.
Comments
Seems by default WWN are used.
I have three tape drives per WWN, so am not getting all necessary nodes.
How can I modify so that Serial Numbers not WWN numbers are used for tape drives?
For example,
root@> inquire
scsidev@0.0.0:SPECTRA PYTHON 2000|Autochanger (Jukebox), /dev/sg0
S/N: 901F002454
ATNN=SPECTRA PYTHON 901F002454
WWNN=201F0090A5002454
scsidev@0.0.1:IBM ULTRIUM-TD4 97F9|Tape, /dev/nst0
S/N: 1011002454
ATNN=IBM ULTRIUM-TD4 1011002454
WWNN=201F0090A5002454
scsidev@0.0.2:IBM ULTRIUM-TD4 97F9|Tape, /dev/nst1
S/N: 1012002454
ATNN=IBM ULTRIUM-TD4 1012002454
WWNN=201F0090A5002454
scsidev@0.1.0:IBM ULTRIUM-TD4 97F9|Tape, /dev/nst2
S/N: 1014002454
ATNN=IBM ULTRIUM-TD4 1014002454
WWNN=201F0090A5002454
scsidev@0.2.0:IBM ULTRIUM-TD4 97F9|Tape, /dev/nst3
S/N: 1021002454
ATNN=IBM ULTRIUM-TD4 1021002454
WWNN=202F0090A5002454
scsidev@0.2.1:IBM ULTRIUM-TD4 97F9|Tape, /dev/nst4
S/N: 1022002454
ATNN=IBM ULTRIUM-TD4 1022002454
WWNN=202F0090A5002454
<snip - removed remaining similar tape drives>
root# > ls -al /dev/tape/by-id/
total 0
drwxr-xr-x 2 root root 180 Jun 4 05:48 .
drwxr-xr-x 3 root root 60 Jun 4 05:36 ..
lrwxrwxrwx 1 root root 9 Jun 4 05:36 scsi-3201f0090a5002454 -> ../../sg0
lrwxrwxrwx 1 root root 10 Jun 4 05:48 scsi-3201f0090a5002454-nst -> ../../nst1
lrwxrwxrwx 1 root root 10 Jun 4 05:48 scsi-3202f0090a5002454-nst -> ../../nst5
lrwxrwxrwx 1 root root 10 Jun 4 05:48 scsi-3203f0090a5002454-nst -> ../../nst6
lrwxrwxrwx 1 root root 10 Jun 4 05:48 scsi-3204f0090a5002454-nst -> ../../nst9
lrwxrwxrwx 1 root root 11 Jun 4 05:48 scsi-3205f0090a5002454-nst -> ../../nst14
lrwxrwxrwx 1 root root 11 Jun 4 05:48 scsi-3206f0090a5002454-nst -> ../../nst16
I assume that the common WWN number is the cause of the missing drive links. Seems to select a random drive from within common WWN numbers, ignoring Serial Number (S/N) and "ATTN" value.