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147 lines
4.9 KiB
Plaintext
147 lines
4.9 KiB
Plaintext
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INTRODUCTION
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------------
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The vblade is a minimal ATA over Ethernet (AoE) storage target. Its
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focus is simplicity, not performance or richness of features. It
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exports a seekable file available over an ethernet local area network
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(LAN) via the AoE data storage protocol.
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The name, "vblade," is historical: It is a virtual EtherDrive (R)
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blade. The first AoE target hardware sold by Coraid was in a blade
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form factor, ten to a 4-rack-unit chassis.
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The seekable file is typically a block device like /dev/md0 but even
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regular files will work. Sparse files can be especially convenient.
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When vblade exports the block storage over AoE it becomes a storage
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target. Another host on the same LAN can access the storage if it has
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a compatible aoe kernel driver.
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BUILDING
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--------
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The following command should build the vblade program on a Linux-based
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system:
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make
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For FreeBSD systems, include an extra parameter like so:
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make PLATFORM=freebsd
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EXAMPLES
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--------
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There is a "vbladed" script that daemonizes the program and sends its
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output to the logger program. Make sure you have logger installed if
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you would like to run vblade as a daemon with the vbladed script.
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ecashin@kokone vblade$ echo 'I have logger' | logger
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ecashin@kokone vblade$ tail -3 /var/log/messages
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Feb 8 14:52:49 kokone -- MARK --
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Feb 8 15:12:49 kokone -- MARK --
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Feb 8 15:19:56 kokone logger: I have logger
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Here is a short example showing how to export a block device with a
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vblade. (This is a loop device backed by a sparse file, but you could
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use any seekable file instead of /dev/loop7.)
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ecashin@kokone vblade$ make
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cc -Wall -c -o aoe.o aoe.c
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cc -Wall -c -o linux.o linux.c
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cc -Wall -c -o ata.o ata.c
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cc -o vblade aoe.o linux.o ata.o
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ecashin@kokone vblade$ su
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Password:
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root@kokone vblade# modprobe loop
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root@kokone vblade# dd if=/dev/zero bs=1k count=1 seek=`expr 1024 \* 4096` of=bd
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-file
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1+0 records in
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1+0 records out
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1024 bytes transferred in 0.009901 seconds (103423 bytes/sec)
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root@kokone vblade# losetup /dev/loop7 bd-file
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root@kokone vblade# ./vblade 9 0 eth0 /dev/loop7
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ioctl returned 0
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4294968320 bytes
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pid 16967: e9.0, 8388610 sectors
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Here's how you can use the Linux aoe driver to access the storage from
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another host on the LAN.
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ecashin@kokone ecashin$ ssh makki
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Last login: Mon Feb 7 10:25:04 2005
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ecashin@makki ~$ su
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Password:
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root@makki ecashin# modprobe aoe
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root@makki ecashin# aoe-stat
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e9.0 eth1 up
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root@makki ecashin# mkfs -t ext3 /dev/etherd/e9.0
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mke2fs 1.35 (28-Feb-2004)
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...
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Creating journal (8192 blocks): done
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Writing superblocks and filesystem accounting information: done
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This filesystem will be automatically checked every 24 mounts or
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180 days, whichever comes first. Use tune2fs -c or -i to override.
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root@makki ecashin# mkdir /mnt/e9.0
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root@makki ecashin# mount /dev/etherd/e9.0 /mnt/e9.0
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root@makki ecashin# echo hooray > /mnt/e9.0/test.txt
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root@makki ecashin# cat /mnt/e9.0/test.txt
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hooray
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Remember: be as careful with these devices as you would with /dev/hda!
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Jumbo Frame Compatibility
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-------------------------
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Vblade can use jumbo frames provided your initiator is jumbo frame
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capable. There is one small configuration gotcha to consider
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to avoid having the vblade kernel frequently drop frames.
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Vblade uses a raw socket to perform AoE. The linux kernel will
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only buffer a certain amount of data for a raw socket. For 2.6
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kernels, this value is managed through /proc:
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root@nai aoe# grep . /proc/sys/net/core/rmem_*
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/proc/sys/net/core/rmem_default:128000
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/proc/sys/net/core/rmem_max:128000
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rmem_max is the max amount a user process may expand the receive
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buffer to -- through setsockopt(...) -- and rmem_default is, as you
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might expect, the default.
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The gotcha is that this amount to buffer does not relate
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to the amount of user data buffered, but the amount of
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real data buffered. As an example, the Intel GbE controller
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must be given 16KB frames to use an MTU over 8KB.
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For each received frame, the kernel must be able to buffer
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16KB, even if the aoe frame is only 60 bytes in length.
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The linux aoe initiator will use 16 outstanding frames when
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used with vblade. A good default for ensuring frames are
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not dropped is to allocate 16KB for 17 frames:
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for f in /proc/sys/net/core/rmem_*; do echo $((17 * 16 * 1024)) >$f; done
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Be sure to start vblade after changing the buffering defaults
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as the buffer value is set when the socket is opened.
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AoE Initiator Compatibility
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---------------------------
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The Linux aoe driver for the 2.6 kernel is compatible if you use
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aoe-2.6-7 or newer. You can use older aoe drivers but you will only
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be able to see one vblade per MAC address.
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Contrib Patches
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---------------
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see contrib/README
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Kvblade
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-------
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While vblade runs as a userland process (like "ls" or "vi"), there
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is another program that runs inside the kernel. It is called
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kvblade. It is alpha software.
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