Dell PowerStore 1200T EMC PowerStore Host Configuration Guide - Page 73

Queue Depth, Setting the Queue Depth, Fast I/O Failure for Fibre Channel Devices

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Queue Depth Follow these recommendations when setting queue depth. NOTE: Changing queue depth settings is designed for advanced users. Increasing the queue depth may cause the host to overstress other clusters that are connected to the AIX host, resulting in performance degradation while communicating with them. Therefore, especially in mixed environments with multiple cluster types that are connected to the AIX host, compare the PowerStore recommendations for queue depth with those of other platforms before applying them. Queue depth is the number of SCSI commands (including I/O requests) that a storage device can handle at a given time. Queue depth can be set on either of the following levels: ● Initiator level - HBA queue depth ● LUN level - LUN queue depth LUN queue depth setting controls the amount of outstanding I/O requests per a single path. HBA queue depth (also referred to as execution throttle) setting controls the number of outstanding requests per HBA port. For optimal operation with PowerStore, it is recommended to adjust the HBA queue depth setting of the FC HBA. The driver module for the card controls LUN queue depth settings at the operating system level. Change the LUN queue depth default value (256) to a lower value only if I/O throttling is required. Setting the Queue Depth Follow these steps to set the HBA queue depth. About this task To set the HBA queue depth: Steps 1. Run the chdev command for each HBA in the AIX host to set the HBA firmware level queue depth: chdev -l fcs# -a num_cmd_elems=2048 -P 2. Reboot the AIX host to apply the HBA queue depth settings. Fast I/O Failure for Fibre Channel Devices This topic describes the Fast I/O Failure feature for FC devices and details the setting recommendations. AIX supports Fast I/O Failure for Fibre Channel devices after link events in a switched environment. When the FC adapter driver detects a link event, such as a lost link between a storage device and a switch, it waits for the fabric to stabilize (approximately 15 s). If the device is not on the fabric, the FC adapter driver fails all new I/Os or future retries of the failed I/Os, until the device rejoins the fabric. The fscsi device attribute fc_err_recov controls Fast I/O Failure (default value is delayed_fail). It is recommended to enable Fast I/O Failure for FC adapters that are connected to PowerStore storage. To enable Fast I/O Failure for all fscsi devices, set the fc_err_recov attribute to fast_fail, as shown in the following example: NOTE: In the example, the fscsi device instance is fscsi0. chdev -l fscsi0 -a fc_err_recov=fast_fail -P Run the following command to verify that the setting was enabled in the ODM: lsattr -El fscsi0 Host Configuration for AIX 73

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Queue Depth
Follow these recommendations when setting queue depth.
NOTE:
Changing queue depth settings is designed for advanced users. Increasing the queue depth may cause the host to
overstress other clusters that are connected to the AIX host, resulting in performance degradation while communicating
with them. Therefore, especially in mixed environments with multiple cluster types that are connected to the AIX host,
compare the PowerStore recommendations for queue depth with those of other platforms before applying them.
Queue depth is the number of SCSI commands (including I/O requests) that a storage device can handle at a given time. Queue
depth can be set on either of the following levels:
●
Initiator level - HBA queue depth
●
LUN level - LUN queue depth
LUN queue depth setting controls the amount of outstanding I/O requests per a single path.
HBA queue depth (also referred to as execution throttle) setting controls the number of outstanding requests per HBA port.
For optimal operation with PowerStore, it is recommended to adjust the HBA queue depth setting of the FC HBA.
The driver module for the card controls LUN queue depth settings at the operating system level. Change the LUN queue depth
default value (256) to a lower value only if I/O throttling is required.
Setting the Queue Depth
Follow these steps to set the HBA queue depth.
About this task
To set the HBA queue depth:
Steps
1.
Run the
chdev
command for each HBA in the AIX host to set the HBA firmware level queue depth:
chdev -l fcs# -a num_cmd_elems=2048 -P
2.
Reboot the AIX host to apply the HBA queue depth settings.
Fast I/O Failure for Fibre Channel Devices
This topic describes the Fast I/O Failure feature for FC devices and details the setting recommendations.
AIX supports Fast I/O Failure for Fibre Channel devices after link events in a switched environment.
When the FC adapter driver detects a link event, such as a lost link between a storage device and a switch, it waits for the
fabric to stabilize (approximately 15 s). If the device is not on the fabric, the FC adapter driver fails all new I/Os or future
retries of the failed I/Os, until the device rejoins the fabric. The fscsi device attribute
fc_err_recov
controls Fast I/O Failure
(default value is
delayed_fail
).
It is recommended to enable Fast I/O Failure for FC adapters that are connected to PowerStore storage.
To enable Fast I/O Failure for all fscsi devices, set the
fc_err_recov
attribute to
fast_fail
, as shown in the following
example:
NOTE:
In the example, the fscsi device instance is fscsi0.
chdev -l fscsi0 -a fc_err_recov=fast_fail -P
Run the following command to verify that the setting was enabled in the ODM:
lsattr -El fscsi0
Host Configuration for AIX
73