"Go live or go home"
If you need to get a lot of data from one AIX host to another, there's
more than one way to do it quickly. During a migration to a new system, you may do a database dump or archive and want to get the data available to the new LPAR within a short time frame. You can
- tweak the network settings
- improve your SAN configuration (just turn on the turbo switch) and
- assign more resources to ease the bottlenecks.
Of course there's Live Partition Mobility (LPM) and various High
Availability options but they may not be suitable for your situation.
Come to think of it, the ones I'm about to suggest may not be suitable for your config, either, but there may be some occasions when these methods will save you big time. That can be the difference between going live and going home defeated.
Getting the files there faster
Here are three ways of speeding up one-off data transfers. Which one you use will depend on your needs (e.g. move or copy data?, two LPARs on the same server?, etc.).
- use the SAN and AIX LVM to migrate an entire volume group from a source to a target host
- create virtual
ethernet adapters for inter-LPAR communication, and
- turn off JFS logging on the target file system.
Whether you use one of these, or something else such as rsync, will
depend on your configuration and your needs.The fine print
Here's a look at each
of the methods in a little more detail.
- Option 1:
Move the LUN from the source LPAR to the target. This allows
you to move, rather than copy, data across the SAN. This requires that
you have a SAN (I thought I'd mention that prereq) and that both the
source and target can connect to the SAN, either via dedicated adapters
or using the VIO server. It also expects that all the data you want to
move, and only that, is contained within a single volume group.
- On the source LPAR you'd need to
the file systems (and release anything else using the VG, such as
- deactivate the volume group using varyoffvg
- export the volume group via exportvg.
- On the SAN, you'd change the map of the LUN from the source to
the target LPAR (needs VIO mapping if you don't have dedicated FC
- On the target LPAR
- Option 2:
Create virtual adapters with their own private VLAN. You can
do that using Dynamic LPAR (DLPAR) from the HMC or IVM. If you're copying across the network, make it virtual and local. A virtual
adapter between two LPARs can use its own private VLAN instead of going
through external physical adapters. This means network traffic will go
at the speed of the bus (not the one I caught yesterday). You need to
address the remote host on its new virtual adapter address. As the VIO
Server wiki explains:
The transmission speed of Virtual Ethernet adapters
is in the range of 1-3 Gigabits per second, depending on the
transmission (MTU) size. The Virtual Ethernet Adapter supports, as
Gigabit (Gb) Ethernet, Standard MTU-Sizes of 1500 Byte and Jumbo frames
with 9000 Byte. Additionally for Gb Ethernet, the MTU-Size of 65280
Bytes is also supported in Virtual Ethernet. So, the MTU of 65280 Bytes
can be only used inside a Virtual Ethernet.
- Option 3: Turn off
JFS logging on the target system. Do you find writing documentation slows you
down? Well, file systems are the same. If you've got a good copy of
your data on the source system, you don't need to trouble the file
system with keeping a record of what it's doing on the target. So for
the period of the copy, you can mount the target file system using
-o log=NULL /dev/targetlv /targetfs
This will make it faster, but speed can be dangerous. If you crash the
LPAR, or the file system loses its metadata consistency, you'd have to
start again from your reliable copy. Once the data has been transferred
successfully, you can unmount and mount the target file system again,
this time with its normal JFS2 log.
There are other methods you could use. It all depends on your needs and
the system configuration.
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