Using ATA Over Ethernet (AoE) on CentOS 7 (Initiator and Target)

This guide explains how you can set up an AoE target and an AoE initiator (client), both running CentOS 7. AoE stands for "ATA over Ethernet" and is a storage area network (SAN) protocol which allows AoE initiators to use storage devices on the (remote) AoE target using normal ethernet cabling. "Remote" in this case means "inside the same LAN" because AoE is not routable outside a LAN (this is a major difference compared to iSCSI). To the AoE initiator, the remote storage looks like a normal, locally-attached hard drive.

 

1 Preliminary Note

I'm using two CentOS 7 servers here:

  • server1.example.com (Initiator): IP address 192.168.1.100
  • server2.example.com (Target): IP address 192.168.1.101

 

2 Enable Additional Repositories

server1/server2:

First, we import the GPG keys for software packages:

rpm --import /etc/pki/rpm-gpg/RPM-GPG-KEY*

Then we enable the EPEL repository on our CentOS system as lots of the packages that we are going to install in the course of this tutorial are not available in the official CentOS 7 repository:

yum -y install epel-release

yum -y install yum-priorities

Edit /etc/yum.repos.d/epel.repo...

nano /etc/yum.repos.d/epel.repo

... and add the line priority=10 to the [epel] section:

[epel]
name=Extra Packages for Enterprise Linux 7 - $basearch
#baseurl=http://download.fedoraproject.org/pub/epel/7/$basearch
mirrorlist=https://mirrors.fedoraproject.org/metalink?repo=epel-7&arch=$basearch
failovermethod=priority
enabled=1
priority=10
gpgcheck=1
gpgkey=file:///etc/pki/rpm-gpg/RPM-GPG-KEY-EPEL-7
[...]

Then we update our existing packages on the system:

yum -y update

3 Loading the AoE Kernel Module on both Systems

server1/server2:

Before we start, we must make sure that the kernel supports AoE:

grep ATA_OVER /boot/config-`uname -r`

This should display something like this:

[[email protected] ~]# grep ATA_OVER /boot/config-`uname -r`
CONFIG_ATA_OVER_ETH=m
[[email protected] ~]#

This means that AoE was built as a kernel module. Let's check if the module is already loaded:

lsmod | grep aoe

If you get nothing back, this means it's not loaded. In this case we can load it as follows:

modprobe aoe

Let's check again if the module is loaded:

lsmod | grep aoe

[[email protected] ~]# lsmod | grep aoe
aoe 54175 0
[[email protected] ~]#

To have the module loaded automatically when the system boots, we add the following line to /etc/rc.local:

nano /etc/rc.local

[...]
modprobe aoe
[...]

 

4 Setting up the Server (Target) on Server 2

server2:

First, we set up the target (server2):

rpm -i http://download.opensuse.org/repositories/home:/cyberorg:/ltsp/CentOS_7/x86_64/vblade-22-3.1.x86_64.rpm

We can use unused logical volumes, image files, hard drives (e.g. /dev/sdb), hard drive partitions (e.g. /dev/sdb1) or RAID devices (e.g. /dev/md0) for the storage. 

In this example, I will use an image file of 10GB that is located in the storage folder /storage.

mkdir /storage
dd if=/dev/zero of=/storage/storage1.img bs=1024k count=10000

This will create an image file /storage/storage1.img with a size of 10GB.

If you want to use logical volume instead, then you can create one with a size of 10GB named storage1 in the volume group vg0 like this:

lvcreate -L10G -n storage1 vg0

Now we export our storage device as follows:

vbladed 0 1 ens33 /storage/storage1.img

The first number (0) is the shelf number (major), the second (1) the slot number (minor), change these numbers to your liking. Each AoE device is identified by a couple major/minor which must be unique (if you are exporting multiple devices), with major between 0-65535 and minor between 0-255. The ens33 part tells vbladed which ethernet device to use, you can find out the details about your ethernet devices by running

ifconfig

).

To start the export automatically whenever you boot the target, open /etc/rc.local...

nano /etc/rc.local

... and add the following line to it (after the modprobe aoe line!):

[...]
vbladed 0 1 ens33 /storage/storage1.img
[...]

 

5 Setting Up the Client (Initiator) on Server 1

server1:

On server1, we install the initiator. There is no package for CentOS 7 available, but the one from centOS 6 works fine, so we will use that here.

rpm -i http://download.opensuse.org/repositories/system:/aoetools/CentOS_CentOS-6/x86_64/aoetools-36-1.2.x86_64.rpm

Now we check what AoE storage devices are available:

aoe-discover

The command

aoe-stat

should now show the storage devices:

[[email protected] ~]# aoe-stat
e0.1 10.485GB ens33 1024 up
[[email protected] ~]#

At this point we have a new block device available on the client box named /dev/etherd/e0.1. If we have a look at the /dev tree a new node appears:

ls -la /dev/etherd/

[[email protected] ~]# ls -la /dev/etherd/
total 0
drwxr-xr-x. 2 root root 160 Jun 30 14:49 .
drwxr-xr-x. 21 root root 3240 Jun 30 14:32 ..
c-w--w----. 1 root disk 152, 3 Jun 30 14:32 discover
brw-rw----. 1 root disk 152, 0 Jun 30 14:49 e0.1
cr--r-----. 1 root disk 152, 2 Jun 30 14:32 err
c-w--w----. 1 root disk 152, 6 Jun 30 14:32 flush
c-w--w----. 1 root disk 152, 4 Jun 30 14:32 interfaces
c-w--w----. 1 root disk 152, 5 Jun 30 14:32 revalidate
[[email protected] ~]#

To use that device, we must format it:

fdisk /dev/etherd/e0.1

[[email protected] ~]# fdisk /dev/etherd/e0.1
Device contains neither a valid DOS partition table, nor Sun, SGI or OSF disklabel
Building a new DOS disklabel with disk identifier 0xed572fd4.
Changes will remain in memory only, until you decide to write them.
After that, of course, the previous content won't be recoverable.


The number of cylinders for this disk is set to 2610.
There is nothing wrong with that, but this is larger than 1024,
and could in certain setups cause problems with:
1) software that runs at boot time (e.g., old versions of LILO)
2) booting and partitioning software from other OSs
   (e.g., DOS FDISK, OS/2 FDISK)
Warning: invalid flag 0x0000 of partition table 4 will be corrected by w(rite)

Command (m for help):
 <-- n
Command action
   e   extended
   p   primary partition (1-4)

<-- p
Partition number (1-4): <-- 1
First sector (2048-20479999, default 2048): <-- ENTER
Using default value 1
Last sector, +sectors or +size{K,M,G} (2048-20479999, default 20479999): <-- ENTER
Using default value 20479999
Partition 1 of type Linux and of size 9.8 GiB is set

Command (m for help):
 <-- t
Selected partition 1
Hex code (type L to list codes):
 <-- L

 0  Empty           1e  Hidden W95 FAT1 80  Old Minix       bf  Solaris
 1  FAT12           24  NEC DOS         81  Minix / old Lin c1  DRDOS/sec (FAT-
 2  XENIX root      39  Plan 9          82  Linux swap / So c4  DRDOS/sec (FAT-
 3  XENIX usr       3c  PartitionMagic  83  Linux           c6  DRDOS/sec (FAT-
 4  FAT16 <32M      40  Venix 80286     84  OS/2 hidden C:  c7  Syrinx
 5  Extended        41  PPC PReP Boot   85  Linux extended  da  Non-FS data
 6  FAT16           42  SFS             86  NTFS volume set db  CP/M / CTOS / .
 7  HPFS/NTFS       4d  QNX4.x          87  NTFS volume set de  Dell Utility
 8  AIX             4e  QNX4.x 2nd part 88  Linux plaintext df  BootIt
 9  AIX bootable    4f  QNX4.x 3rd part 8e  Linux LVM       e1  DOS access
 a  OS/2 Boot Manag 50  OnTrack DM      93  Amoeba          e3  DOS R/O
 b  W95 FAT32       51  OnTrack DM6 Aux 94  Amoeba BBT      e4  SpeedStor
 c  W95 FAT32 (LBA) 52  CP/M            9f  BSD/OS          eb  BeOS fs
 e  W95 FAT16 (LBA) 53  OnTrack DM6 Aux a0  IBM Thinkpad hi ee  GPT
 f  W95 Ext'd (LBA) 54  OnTrackDM6      a5  FreeBSD         ef  EFI (FAT-12/16/
10  OPUS            55  EZ-Drive        a6  OpenBSD         f0  Linux/PA-RISC b
11  Hidden FAT12    56  Golden Bow      a7  NeXTSTEP        f1  SpeedStor
12  Compaq diagnost 5c  Priam Edisk     a8  Darwin UFS      f4  SpeedStor
14  Hidden FAT16 <3 61  SpeedStor       a9  NetBSD          f2  DOS secondary
16  Hidden FAT16    63  GNU HURD or Sys ab  Darwin boot     fb  VMware VMFS
17  Hidden HPFS/NTF 64  Novell Netware  b7  BSDI fs         fc  VMware VMKCORE
18  AST SmartSleep  65  Novell Netware  b8  BSDI swap       fd  Linux raid auto
1b  Hidden W95 FAT3 70  DiskSecure Mult bb  Boot Wizard hid fe  LANstep
1c  Hidden W95 FAT3 75  PC/IX           be  Solaris boot    ff  BBT
Hex code (type L to list codes):
 <-- 83

Command (m for help): <-- w
The partition table has been altered!

Calling ioctl() to re-read partition table.
Syncing disks.
[[email protected] ~]#

Afterwards, there's a new device /dev/etherd/e0.1p1 which you can see in the output of

ls -l /dev/etherd/

[[email protected] ~]# ls -l /dev/etherd/
total 0
c-w--w----. 1 root disk 152, 3 Jun 30 14:32 discover
brw-rw----. 1 root disk 152, 0 Jun 30 14:54 e0.1
brw-rw----. 1 root disk 152, 1 Jun 30 14:54 e0.1p1
cr--r-----. 1 root disk 152, 2 Jun 30 14:32 err
c-w--w----. 1 root disk 152, 6 Jun 30 14:32 flush
c-w--w----. 1 root disk 152, 4 Jun 30 14:32 interfaces
c-w--w----. 1 root disk 152, 5 Jun 30 14:32 revalidate
[[email protected] ~]#

Now we create a filesystem on /dev/etherd/e0.1p1...

mkfs.ext4 /dev/etherd/e0.1p1

... and mount it for test purposes:

mount /dev/etherd/e0.1p1 /mnt

You should now see the new device in the outputs of...

mount

[[email protected] ~]# mount
sysfs on /sys type sysfs (rw,nosuid,nodev,noexec,relatime,seclabel)
proc on /proc type proc (rw,nosuid,nodev,noexec,relatime)
devtmpfs on /dev type devtmpfs (rw,nosuid,seclabel,size=930336k,nr_inodes=232584,mode=755)
securityfs on /sys/kernel/security type securityfs (rw,nosuid,nodev,noexec,relatime)
tmpfs on /dev/shm type tmpfs (rw,nosuid,nodev,seclabel)
devpts on /dev/pts type devpts (rw,nosuid,noexec,relatime,seclabel,gid=5,mode=620,ptmxmode=000)
tmpfs on /run type tmpfs (rw,nosuid,nodev,seclabel,mode=755)
tmpfs on /sys/fs/cgroup type tmpfs (ro,nosuid,nodev,noexec,seclabel,mode=755)
cgroup on /sys/fs/cgroup/systemd type cgroup (rw,nosuid,nodev,noexec,relatime,xattr,release_agent=/usr/lib/systemd/systemd-cgroups-agent,name=systemd)
pstore on /sys/fs/pstore type pstore (rw,nosuid,nodev,noexec,relatime)
cgroup on /sys/fs/cgroup/cpu,cpuacct type cgroup (rw,nosuid,nodev,noexec,relatime,cpuacct,cpu)
cgroup on /sys/fs/cgroup/memory type cgroup (rw,nosuid,nodev,noexec,relatime,memory)
cgroup on /sys/fs/cgroup/devices type cgroup (rw,nosuid,nodev,noexec,relatime,devices)
cgroup on /sys/fs/cgroup/hugetlb type cgroup (rw,nosuid,nodev,noexec,relatime,hugetlb)
cgroup on /sys/fs/cgroup/net_cls type cgroup (rw,nosuid,nodev,noexec,relatime,net_cls)
cgroup on /sys/fs/cgroup/freezer type cgroup (rw,nosuid,nodev,noexec,relatime,freezer)
cgroup on /sys/fs/cgroup/perf_event type cgroup (rw,nosuid,nodev,noexec,relatime,perf_event)
cgroup on /sys/fs/cgroup/blkio type cgroup (rw,nosuid,nodev,noexec,relatime,blkio)
cgroup on /sys/fs/cgroup/cpuset type cgroup (rw,nosuid,nodev,noexec,relatime,cpuset)
configfs on /sys/kernel/config type configfs (rw,relatime)
/dev/mapper/centos-root on / type xfs (rw,relatime,seclabel,attr2,inode64,noquota)
selinuxfs on /sys/fs/selinux type selinuxfs (rw,relatime)
systemd-1 on /proc/sys/fs/binfmt_misc type autofs (rw,relatime,fd=30,pgrp=1,timeout=300,minproto=5,maxproto=5,direct)
debugfs on /sys/kernel/debug type debugfs (rw,relatime)
mqueue on /dev/mqueue type mqueue (rw,relatime,seclabel)
hugetlbfs on /dev/hugepages type hugetlbfs (rw,relatime,seclabel)
/dev/sda1 on /boot type xfs (rw,relatime,seclabel,attr2,inode64,noquota)
tmpfs on /run/user/0 type tmpfs (rw,nosuid,nodev,relatime,seclabel,size=188060k,mode=700)
/dev/etherd/e0.1p1 on /mnt type ext4 (rw,relatime,seclabel,data=ordered)
[[email protected] ~]#

... and

df -h

[[email protected] ~]# df -h
Filesystem Size Used Avail Use% Mounted on
/dev/mapper/centos-root 28G 1.3G 27G 5% /
devtmpfs 909M 0 909M 0% /dev
tmpfs 919M 0 919M 0% /dev/shm
tmpfs 919M 8.6M 910M 1% /run
tmpfs 919M 0 919M 0% /sys/fs/cgroup
/dev/sda1 497M 192M 306M 39% /boot
tmpfs 184M 0 184M 0% /run/user/0
/dev/etherd/e0.1p1 9.5G 37M 9.0G 1% /mnt
[[email protected] ~]#

You can unmount it like this:

umount /mnt

To have the device mounted automatically at boot time, e.g. in the directory /storage, we create that directory...

mkdir /storage

... and add the following line to /etc/fstab:

nano /etc/fstab

[...]
/dev/etherd/e0.1p1       /storage        ext4    defaults,auto,_netdev 0 0

This alone isn't enough to have the device mounted at boot time because the AoE stuff gets loaded after /etc/fstab is read. Therefore we open /etc/rc.local...

nano /etc/rc.local

... and add the following lines to it (after the modprobe aoe line!):

[...]
aoe-discover
sleep 5
mount -a
[...]

For test purposes, you can now reboot the system:

reboot

After the reboot, the device should be mounted:

mount

[[email protected] ~]# mount
sysfs on /sys type sysfs (rw,nosuid,nodev,noexec,relatime,seclabel)
proc on /proc type proc (rw,nosuid,nodev,noexec,relatime)
devtmpfs on /dev type devtmpfs (rw,nosuid,seclabel,size=930336k,nr_inodes=232584,mode=755)
securityfs on /sys/kernel/security type securityfs (rw,nosuid,nodev,noexec,relatime)
tmpfs on /dev/shm type tmpfs (rw,nosuid,nodev,seclabel)
devpts on /dev/pts type devpts (rw,nosuid,noexec,relatime,seclabel,gid=5,mode=620,ptmxmode=000)
tmpfs on /run type tmpfs (rw,nosuid,nodev,seclabel,mode=755)
tmpfs on /sys/fs/cgroup type tmpfs (ro,nosuid,nodev,noexec,seclabel,mode=755)
cgroup on /sys/fs/cgroup/systemd type cgroup (rw,nosuid,nodev,noexec,relatime,xattr,release_agent=/usr/lib/systemd/systemd-cgroups-agent,name=systemd)
pstore on /sys/fs/pstore type pstore (rw,nosuid,nodev,noexec,relatime)
cgroup on /sys/fs/cgroup/cpu,cpuacct type cgroup (rw,nosuid,nodev,noexec,relatime,cpuacct,cpu)
cgroup on /sys/fs/cgroup/memory type cgroup (rw,nosuid,nodev,noexec,relatime,memory)
cgroup on /sys/fs/cgroup/devices type cgroup (rw,nosuid,nodev,noexec,relatime,devices)
cgroup on /sys/fs/cgroup/hugetlb type cgroup (rw,nosuid,nodev,noexec,relatime,hugetlb)
cgroup on /sys/fs/cgroup/net_cls type cgroup (rw,nosuid,nodev,noexec,relatime,net_cls)
cgroup on /sys/fs/cgroup/freezer type cgroup (rw,nosuid,nodev,noexec,relatime,freezer)
cgroup on /sys/fs/cgroup/perf_event type cgroup (rw,nosuid,nodev,noexec,relatime,perf_event)
cgroup on /sys/fs/cgroup/blkio type cgroup (rw,nosuid,nodev,noexec,relatime,blkio)
cgroup on /sys/fs/cgroup/cpuset type cgroup (rw,nosuid,nodev,noexec,relatime,cpuset)
configfs on /sys/kernel/config type configfs (rw,relatime)
/dev/mapper/centos-root on / type xfs (rw,relatime,seclabel,attr2,inode64,noquota)
selinuxfs on /sys/fs/selinux type selinuxfs (rw,relatime)
systemd-1 on /proc/sys/fs/binfmt_misc type autofs (rw,relatime,fd=30,pgrp=1,timeout=300,minproto=5,maxproto=5,direct)
debugfs on /sys/kernel/debug type debugfs (rw,relatime)
mqueue on /dev/mqueue type mqueue (rw,relatime,seclabel)
hugetlbfs on /dev/hugepages type hugetlbfs (rw,relatime,seclabel)
/dev/sda1 on /boot type xfs (rw,relatime,seclabel,attr2,inode64,noquota)
tmpfs on /run/user/0 type tmpfs (rw,nosuid,nodev,relatime,seclabel,size=188060k,mode=700)
/dev/etherd/e0.1p1 on /mnt type ext4 (rw,relatime,seclabel,data=ordered)
[[email protected] ~]#

df -h

[[email protected] ~]# df -h
Filesystem Size Used Avail Use% Mounted on
/dev/mapper/centos-root 28G 1.3G 27G 5% /
devtmpfs 909M 0 909M 0% /dev
tmpfs 919M 0 919M 0% /dev/shm
tmpfs 919M 8.6M 910M 1% /run
tmpfs 919M 0 919M 0% /sys/fs/cgroup
/dev/sda1 497M 192M 306M 39% /boot
tmpfs 184M 0 184M 0% /run/user/0
/dev/etherd/e0.1p1 9.5G 37M 9.0G 1% /mnt
[[email protected] ~]#

 

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