Overview: The Next Generation Mass Storage Stack (September 2009)

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SCSI ATTRIBUTES FOR LUN PATH : 0/2/1/0.0x500805f300083899.0x4011000000000000
name = lunid
current =0x4011000000000000 (LUN # 17, Flat Space Addressing)
default =
saved =
Selecting Load Balancing Algorithms
By setting the load_bal_policy attribute, you can select one of the following load balancing algorithms:
least_cmd_load
Directs I/O requests through the hardware path with the least outstanding I/O requests.
round_robin
Cycles I/O requests through the available hardware paths in round robin fashion.
cl_round_robin
Cycles I/O requests through the available hardware paths in round robin fashion, within
the locality of CPU on which the I/O was initiated. This is known as cell-aware round robin.
weighted_rr
Cycles I/O requests through the available hardware paths in round robin fashion, subject
to a user-assigned weight for each path. A hardware path is used until the number of I/O
requests matches its “weight”, and then another path is chosen.
preferred_path
Directs I/O requests to the specified hardware path, if available.
pref_tport
Directs I/O requests to the specified target port, if available.
closest_path
Directs I/O requests through the hardware path with the lowest memory access latency,
based on its affinity with the CPU processing the I/O operation.
path_lockdown
Directs I/O requests through a single hardware path. By default, the mass storage
subsystem internally determines the optimal lunpath. The administrator can manually set the
lunpath with the lpt_to_lockdown attribute. The lpt_to_lockdown attribute must only be set
when the device is in the UNOPEN state. This algorithm is the only one supported for serial
devices such as tape drives, changers, and SCSI controller devices, and does not apply to
block devices such as disks.
To retrieve the load balancing policy for a LUN, enter the following command:
# scsimgr get_attr -D /dev/rdisk/disk49 –a load_bal_policy
SCSI ATTRIBUTES FOR LUN : /dev/rdisk/disk49
name = load_bal_policy
current = least_cmd_load
default = least_cmd_load
saved =
To choose the least_cmd_load policy for all disks, set the scope for all SCSI disks using the following
command:
# scsimgr set_attr –N /esci/esdisk –a load_bal_policy=least_cmd_load
Value of attribute load_bal_policy set successfully
To choose the round_robin policy for all HP disks, set the scope for all SCSI disks with a vendor identifier of
"HP " using the following command:
# scsimgr set_attr –N "/escsi/esdisk/0x0/HP " –a load_bal_policy=round_robin
Value of attribute load_bal_policy set successfully
To choose the round_robin policy for a single LUN, use the following command:
# scsimgr set_attr –D /dev/rdisk/disk49 –a load_bal_policy=round_robin
Value of attribute load_bal_policy set successfully