Bug 821390 - Not all the usb disks are managed by multipath
Not all the usb disks are managed by multipath
Product: Red Hat Enterprise Linux 6
Classification: Red Hat
Component: ovirt-node (Show other bugs)
Unspecified Unspecified
medium Severity medium
: rc
: ---
Assigned To: Mike Burns
Virtualization Bugs
Depends On:
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Reported: 2012-05-14 06:23 EDT by yuanquan chen
Modified: 2016-04-26 10:33 EDT (History)
10 users (show)

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Fixed In Version:
Doc Type: Bug Fix
Doc Text:
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Clone Of:
Last Closed: 2012-05-14 07:41:53 EDT
Type: Bug
Regression: ---
Mount Type: ---
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oVirt Team: ---
RHEL 7.3 requirements from Atomic Host:
Cloudforms Team: ---

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Description yuanquan chen 2012-05-14 06:23:53 EDT
Description of problem:
Some usb disk can be managed under multipath, while others can't be.

Version-Release number of selected component (if applicable):

How reproducible:

Steps to Reproduce:
1. boot from bootable media or intalled rhev-h
2. add a SanDisk Cruzer Edge 16GB and a Kingston 8GB usb disk to machine
3. drop to shell, execute "multipath -ll; ls /dev/mapper/"
Actual results:
Some usb disks are managed by multipath, some are not managed.

[root@localhost admin]# ls /dev/sd
sda   sda1  sda2  sda3  sda4  sdb   sdb1  sdc   sdc1  
[root@localhost admin]# multipath -ll
1SanDisk dm-10 SanDisk,Cruzer Edge
size=15G features='0' hwhandler='0' wp=rw
`-+- policy='round-robin 0' prio=1 status=active
  `- 6:0:0:0 sdb 8:16 active ready running
1ATA_ST3500413AS_S2A1NJ08 dm-0 ATA,ST3500413AS
size=466G features='0' hwhandler='0' wp=rw
`-+- policy='round-robin 0' prio=1 status=active
  `- 0:0:0:0 sda 8:0  active ready running
[root@localhost admin]#  

Expected results:
All the usb disks should be managed by multipath or not. The multipath management of usb disks should be consistent.

Additional info:
Comment 2 Mike Burns 2012-05-14 07:41:53 EDT
This is a limitation of the usb disks themselves, not ovirt-node.  Older USB sticks don't respon to scsi_id calls and cannot be management by multipath.  Newer usb sticks do work correctly with multipath and get picked up correctly.  The only way to make it consistent would be to stop multipath from all usb sticks (not even sure that will work) but that's not optimal.  The rule we follow is that we use multipath for devices that we can, and fall back to /dev/sd* when we can't.

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