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Description of problem: Currently there is no entry for blacklisting of scsi devices in the default templates of multipath package. This makes the user assume to use the following setting convention (which is in the template for ide drives) for scsi devices also. ^hd[a-z] The problem is that the same setting for a scsi device can be problematic: ^sd[a] leads both to sda, sdaa, sdab .... Hence it blacklists other devices where we only wanted to blacklist the single local sda scsi device. We propose the inclusion of the following settings in the default templates for multipath.conf to assist users. sda$ which specifically means to blacklist only and only the sda device. How reproducible: Always Steps to Reproduce: 1. Add as many devices till sdz is reached. the next device would be sdaa 2. Try blacklisting the devices, devnode "sda" 3. It blacklists all devices starting with sda. Actual results: It is blacklisting all devices all devices starting with sda Expected results: Should blacklist only device sda. Additional info:
People shouldn't blacklist individual devices this way. Using the devnode method of blacklisting is fine for knocking out whole types of devices, but since there is no guarantee that the device registered as /dev/sda on one boot will be registered as /dev/sda on the next, blacklisting individual devices by devnode is risky and not recommended. People should blacklist the devices by wwid instead. I realize that people don't do this often, and unless new devices are added, it's really almost never a problem to use the devnode method, but it's still not ideal. I suppose that I should add a comment saying something like this to the /etc/multipath.conf.
Thats right. It does make a lot of sense blacklisting devices using the WWID instead of device names in the multipath.conf file. I am aware of the 'scsi_id' command which can be used to retrieve the WWID of a SCSI device as in: 'scsi_id -p 0x83 -g -s /block/<SCSI device> But this command does not always work for local disks (which need blacklisting). On one of my hosts, the above command gave a blank output. On another one, it gave the following output: [root@lnx200-127 ~]# scsi_id -p 0x83 -g -s /block/sda 0:0:0:0: sg_io failed status 0x8 0x0 0x0 0x2 0:0:0:0: sense key 0x5 ASC 0x24 ASCQ 0x0 0:0:0:0: Unable to get INQUIRY vpd 1 page 0x83. So is there any simple foolproof method to obtain the WWID of a SCSI device?
Apparently "scsi_id -g -u -s /block/<SCSI device>" seems to work fine for all cases including the ones described above. The unique device id generated by this command could be used for blacklisting SCSI disks in the multipath.conf file.
An advisory has been issued which should help the problem described in this bug report. This report is therefore being closed with a resolution of ERRATA. For more information on the solution and/or where to find the updated files, please follow the link below. You may reopen this bug report if the solution does not work for you. http://rhn.redhat.com/errata/RHEA-2007-0256.html