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Man Pages

Manual Reference Pages  -  AOE (4)


aoe, aoed - ATA over Ethernet (AoE) device driver


Sysctl Variables


To compile this driver into the kernel, place the following line in your kernel configuration file:

.Cd device aoe

Alternatively, to load the driver as a module at boot time, place the following line in the loader.conf(5):

.Cd aoe_load= YES


The aoe driver enables access to AoE devices on a network by making them appear as locally-attached disks.

AoE works by packaging the ATA registers -- and data if necessary -- into Ethernet request/response frames. The driver will detect the use of jumbo frames and resize the request payload to maximum size that can be used.

The aoe driver has a mechanism for retransmitting frames which do not receive a response. Each aoe kernel device maintains a round-trip average of the time between when a request is sent and its response is received. Whenever a request has been outstanding for 150% of this average, it is retransmitted and the average is backed off by a multiple of two.

When a request has been outstanding for
.Cd maxwait time, the device is considered gone and is flagged as down. If the device is not currently open, it is immediately removed from the system. If the device is open, it will be removed on final close. A device cannot come back up until it is removed from the system and a new discover sequence has been done.
.Cd Maxwait defaults to 180s and is settable by a sysctl.

The aoe driver must be told what ethernet interfaces are acceptable for AoE traffic. This is accomplished by setting a sysctl string that contains a space separated list of interface names.

Once the list of valid interfaces is set, the aoe driver must be told to probe the network for AoE devices. This is accomplished by setting the sysctl integer
.Cd discover .


The following are available as sysctl(8) variables:

A read-write string containing a space separated list of network interface names valid for AoE.


An integer that specifies the number of seconds to wait for an outstanding AoE request to be completed before failing a device.


An integer that specifies whether or not the ATA disks attached to all AoE devices should have the write cache enabled. Transitions in the state of this variable will cause all AoE devices to be flagged for enable/disable of the write cache on the next I/O operation. The write cache is not affected immediately for driver simplicity. To force the write cache action, do at least one read from each device after setting/clearing this variable. The write cache is enabled by default.


A read-only string containing the devices the aoe driver knows about, one per line.


% ls /dev/aoed*
ls: /dev/aoed*: No such file or directory
% kldload aoe
% sysctl net.aoe
net.aoe.maxwait: 180
net.aoe.wc: 1
% sysctl net.aoe.iflist=xl0
net.aoe.iflist:  -> xl0
% sysctl net.aoe
net.aoe.iflist: xl0
net.aoe.maxwait: 180
net.aoe.wc: 1
aoed10        xl0    UP
aoed3         xl0    UP
aoed30        xl0    UP
% ls -l /dev/aoed*
crw-r-----  1 root  operator    0, 153 Oct 12 17:10 /dev/aoed10
crw-r-----  1 root  operator    0, 154 Oct 12 17:10 /dev/aoed10s1
crw-r-----  1 root  operator    0, 155 Oct 12 17:10 /dev/aoed10s1a
crw-r-----  1 root  operator    0, 156 Oct 12 17:10 /dev/aoed10s1c
crw-r-----  1 root  operator    0, 152 Oct 12 17:10 /dev/aoed3
crw-r-----  1 root  operator    0, 151 Oct 12 17:10 /dev/aoed30


Each aoe device node created in a system is comprised of aoed + system unit number. The unit numbers used by aoe are created by the relation:

.Cd unit = aoemajor * 10 + aoeminor

This simple relation makes it very easy for administrators to associate blades in a shelf with nodes in the system. In the example above, there are three blades; one each in shelf 1 / slot 0, shelf 0 / slot 3, and shelf 3 / slot 0.

When an AoE device is powered up it broadcasts a message so hosts may automatically acknowledge its existence.


/dev/aoed* AoE disk device nodes


.An Sam Hopkins <>.
.An Stacey D. Son <>.


No MTU path discovery is done and, therefore, it is assumed that the aoe initiator, target, and all devices between are correctly configured with the same MTU.
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