Multipathd Daemon was Unable to Set Options "fast_io_fail_tmo" or "dev_loss_tmo" Under UEK1 or RHCK

该博客针对Oracle Linux 5.7 - 5.10系统，在UEK1或RHCK内核下，/etc/multipath.conf中设置的fast_io_fail_tmo和dev_loss_tmo参数重启后未生效的问题进行分析。指出这是已知缺陷，在特定版本已修复，还介绍了参数含义及算法，并给出升级RPM包的解决办法。

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Multipathd Daemon was Unable to Set Options "fast_io_fail_tmo" or "dev_loss_tmo" Under UEK1 or RHCK (文档 ID 1678794.1)

APPLIES TO:

Linux OS - Version Oracle Linux 5.7 with Unbreakable Enterprise Kernel [2.6.32] to Oracle Linux 5.10 with Unbreakable Enterprise Kernel [2.6.32] [Release OL5U7 to OL5U10]
Linux OS - Version Oracle Linux 5.7 to Oracle Linux 5.10 [Release OL5U7 to OL5U10]
Oracle Cloud Infrastructure - Version N/A and later
Linux x86
Linux x86-64

SYMPTOMS

Under UEK1 kernel or RHCK kernel, set options "fast_io_fail_tmo" and "dev_loss_tmo" in /etc/multipath.conf:

dev_loss_tmo 95
fast_io_fail_tmo 5

No override of default values for those sysfs parameters as configured in /etc/multipath.conf after reboot system:

# cat /sys/class/fc_remote_ports/rport*/dev_loss_tmo
30
30
30
30
30
30
30
30
30
30
30
30
.
# cat /sys/class/fc_remote_ports/rport*/fast_io_fail_tmo
off
off
off
off
off
off
off
off
off
off
off
off

CAUSE

This is known defect. Issue fixed on device-mapper-multipath-0.4.9-64.0.9.el5 and later.

SOLUTION

Note:
Options "fast_io_fail_tmo" and "dev_loss_tmo" were introducted into /etc/multipath.conf configuration file as new defaults from device-mapper-multipath-0.4.7-46.el5.

Specify the "fast_io_fail_tmo" option to set time waits of the SCSI layer to fail back the I/O after a SCSI device fails. The valid scope of this option could be "off" or any number smaller than the "dev_loss_tmo" option.
Specify the "dev_loss_tmo" option to set time waits of the SCSI layer to mark a SCSI device failed after it fails.

The algorithm of "dev_loss_tmo" affecting value is dev_loss_tmo = MAX(no_path_retry * polling_internal, dev_loss_tmo), for instance:

no_path_retry 5
polling_interval 30
dev_loss_tmo 95

Then the affecting value of "dev_loss_tmo" will be 5*30=150, NOT 95.

Upgrade device-mapper-multipath RPM package to device-mapper-multipath-0.4.9-64.0.9.el5 or later with its dependencies via YUM.

# yum update device-mapper-multipath

Note: device-mapper-multipath-0.4.9-64.0.9.el5 and its dependencies are available in Channels: Oracle Linux 5 Update 10 Patch (x86_64)/(i386) and Oracle Linux 5 Latest (x86_64)/(i386).