vblade

INTRODUCTION
------------

The vblade is a minimal ATA over Ethernet (AoE) storage target. Its
focus is simplicity, not performance or richness of features. It
exports a seekable file available over an ethernet local area network
(LAN) via the AoE data storage protocol.

The name, "vblade," is historical: It is a virtual EtherDrive (R)
blade. The first AoE target hardware sold by Coraid was in a blade
form factor, ten to a 4-rack-unit chassis.

The seekable file is typically a block device like /dev/md0 but even
regular files will work. Sparse files can be especially convenient.
When vblade exports the block storage over AoE it becomes a storage
target. Another host on the same LAN can access the storage if it has
a compatible aoe kernel driver.

BUILDING
--------

The following command should build the vblade program on a Linux-based
system:

make

For FreeBSD systems, include an extra parameter like so:

make PLATFORM=freebsd

EXAMPLES
--------

There is a "vbladed" script that daemonizes the program and sends its
output to the logger program. Make sure you have logger installed if
you would like to run vblade as a daemon with the vbladed script.

ecashin@kokone vblade$ echo 'I have logger' | logger
ecashin@kokone vblade$ tail -3 /var/log/messages
Feb 8 14:52:49 kokone -- MARK --
Feb 8 15:12:49 kokone -- MARK --
Feb 8 15:19:56 kokone logger: I have logger

Here is a short example showing how to export a block device with a
vblade. (This is a loop device backed by a sparse file, but you could
use any seekable file instead of /dev/loop7.)

ecashin@kokone vblade$ make
cc -Wall -c -o aoe.o aoe.c
cc -Wall -c -o linux.o linux.c
cc -Wall -c -o ata.o ata.c
cc -o vblade aoe.o linux.o ata.o
ecashin@kokone vblade$ su
Password:
root@kokone vblade# modprobe loop
root@kokone vblade# dd if=/dev/zero bs=1k count=1 seek=`expr 1024 \* 4096` of=bd
-file
1+0 records in
1+0 records out
1024 bytes transferred in 0.009901 seconds (103423 bytes/sec)
root@kokone vblade# losetup /dev/loop7 bd-file
root@kokone vblade# ./vblade 9 0 eth0 /dev/loop7
ioctl returned 0
4294968320 bytes
pid 16967: e9.0, 8388610 sectors

Here's how you can use the Linux aoe driver to access the storage from
another host on the LAN.

ecashin@kokone ecashin$ ssh makki
Last login: Mon Feb 7 10:25:04 2005
ecashin@makki ~$ su
Password:
root@makki ecashin# modprobe aoe
root@makki ecashin# aoe-stat
e9.0 eth1 up
root@makki ecashin# mkfs -t ext3 /dev/etherd/e9.0
mke2fs 1.35 (28-Feb-2004)
...
Creating journal (8192 blocks): done
Writing superblocks and filesystem accounting information: done

This filesystem will be automatically checked every 24 mounts or
180 days, whichever comes first. Use tune2fs -c or -i to override.
root@makki ecashin# mkdir /mnt/e9.0
root@makki ecashin# mount /dev/etherd/e9.0 /mnt/e9.0
root@makki ecashin# echo hooray > /mnt/e9.0/test.txt
root@makki ecashin# cat /mnt/e9.0/test.txt
hooray

Remember: be as careful with these devices as you would with /dev/hda!

Jumbo Frame Compatibility
-------------------------

Vblade can use jumbo frames provided your initiator is jumbo frame
capable. There is one small configuration gotcha to consider
to avoid having the vblade kernel frequently drop frames.

Vblade uses a raw socket to perform AoE. The linux kernel will
only buffer a certain amount of data for a raw socket. For 2.6
kernels, this value is managed through /proc:

root@nai aoe# grep . /proc/sys/net/core/rmem_*
/proc/sys/net/core/rmem_default:128000
/proc/sys/net/core/rmem_max:128000

rmem_max is the max amount a user process may expand the receive
buffer to -- through setsockopt(...) -- and rmem_default is, as you
might expect, the default.

The gotcha is that this amount to buffer does not relate
to the amount of user data buffered, but the amount of
real data buffered. As an example, the Intel GbE controller
must be given 16KB frames to use an MTU over 8KB.
For each received frame, the kernel must be able to buffer
16KB, even if the aoe frame is only 60 bytes in length.

The linux aoe initiator will use 16 outstanding frames when
used with vblade. A good default for ensuring frames are
not dropped is to allocate 16KB for 17 frames:

for f in /proc/sys/net/core/rmem_*; do echo $((17 * 16 * 1024)) >$f; done

Be sure to start vblade after changing the buffering defaults
as the buffer value is set when the socket is opened.

AoE Initiator Compatibility
---------------------------

The Linux aoe driver for the 2.6 kernel is compatible if you use
aoe-2.6-7 or newer. You can use older aoe drivers but you will only
be able to see one vblade per MAC address.

Contrib Patches
---------------

see contrib/README

Kvblade
-------

While vblade runs as a userland process (like "ls" or "vi"), there
is another program that runs inside the kernel. It is called
kvblade. It is alpha software.