Red Hat DEVICE-MAPPER MULTIPATH 5.2 Manual do Utilizador descarregar pdf (Página 20)

DotHill – Linux Device Mapper Multipath “How To” for Storage Revision 4

# multipath -ll

yourspace (3600c0ff0000000000234320d5321e101)

[size=25 GB][features="0"][hwhandler="0"]

\_ round-robin 0 [prio=1][active]

\_ 2:0:0:1 sdc 8:32 [active][ready]

\_ round-robin 0 [prio=1][enabled]

\_ 3:0:0:1 sdf 8:80 [active][ready]

myspace (3600c0ff000000000023432491536d600)

[size=33 GB][features="0"][hwhandler="0"]

\_ round-robin 0 [prio=1][active]

\_ 2:0:1:0 sdd 8:48 [active][ready]

\_ round-robin 0 [prio=1][enabled]

\_ 3:0:1:0 sdg 8:96 [active][ready]

The multipath devices are created in the /dev/mapper directory. These devices can be used like

any other block devices present in the host for any block- or file-level I/O operations.

The state of the path is given as [ready] [active] if the path is up and ready for I/O. If the

path is down, this state will be shown as [faulty] [failed]. The path states will be updated

periodically by multipathd based on the polling interval specified in /etc/multipath.conf.

If you want to reduce the number assigned to the /dev/mapper/mpath link, you can edit the

“/var/lib/multipath/binding” file. Just delete the uncommented wwid/alias lines in the file.

9 Known Issues

Following are the limitations and known issues of Device Mapper Multipath:

• ioctl support is not available on a multipath device created by DM-MP. Hence SCSI inquiry

like operations are not possible with these devices

• You have to manually enter the device properties for the SANnet arrays in the

/etc/multipath.conf file.

• Under all path failure condition, if the queue_if_no_path feature is enabled, the I/O

requests are queued as long as system resources are available. This may result in system

resource starvation.

• Wild card or regular expression support for the product and vendor string (in the

/etc/multipath.conf file) is only supported in RHEL 4 U3

• Time based I/O request queuing (

no_path_retry in the /etc/multipath.conf file) is only

supported in RHEL4U3.

• Device Mapper Multipath may fail to create device nodes for partitions when the

configuration has a large number of LUNs

• For a host with many LUNs, the command multipath -ll may take longer time to display

the status of all the DM-MP devices if there is a change in the path status

• Device Mapper Multipath does not support online deletion of multipath devices. If the

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Red Hat DEVICE-MAPPER MULTIPATH 5.2 Manual do Utilizador Página 20