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Wed, 18 Feb 2009

/Hosting/Amazon/EBS: Keep Your Amazon Server's Data on EBS

Amazon's EC2 servers do not provide persistent storage. If the server is turned off or even perhaps halted, then all data since the server was initialized is lost. (I am pretty sure one can reboot an Amazon server without losing data, but have not tried....)

Therefore, at the least, all volatile data should be stored on an Amazon "Elastic Block Storage" (EBS) volume. As a further incentive, Amazon says[1] that EBS is faster then the storage associated directly with an Amazon server, and that it is replicated across multiple servers in the data center. The downside, of course, is that you pay for EBS, both by gigabyte per month and by I/O per month.

Here[2] is an excellent tutorial on how to use EBS with a MySQL database, and here[3] is a nice general introduction.

I am going to move my Amazon Server's /var/www/ onto EBS. First use ec2-describe-instances to find out which Amazon zone the server is located in[4]: us-east-1c. Now create a 5G EBS volume:

ec2-create-volume -z us-east-1c -s 5

From what I can see so far, changing the volume size probably involves snapshotting the volume, and then restoring the snapshot to a bigger volume. This small headache must be traded-off against the EBS cost of 10 cents per gigabyte per month.

ec2-describe-volumes will tell you when the new volume is available. Now attach the volume to the server instance at /dev/sdz:

ec2-attach-volume -d /dev/sdz -i i-c1a320a8 vol-3159bd58

Now login to the server and format the volume:

mkfs.ext3 /dev/sdz

(Note that xfs has apparently been a popular format choice in the past because of its explicit freezability for snapshots, but I have seen in more then one place now that Amazon EC2 has problems with xfs.)

Setup /etc/fstab by adding the following entry:

/dev/sdz /vol ext3 noatime 0 0

And mount the volume:

cd /
mkdir vol
mount vol

Now move the contents of /var/www to the volume:

/etc/init.d/apache2 stop
cd /var
mv www /vol/
ln -s /vol/www/ www
/etc/init.d/apache2 start

[1] http://aws.amazon.com/ebs/
[2] http://developer.amazonwebservices.com/connect/entry.jspa?externalID=1663
[3] http://blog.rightscale.com/2008/08/20/amazon-ebs-explained/
[4] http://developer.amazonwebservices.com/connect/entry.jspa?externalID=1347

posted at: 07:35 | path: /Hosting/Amazon/EBS | permanent link to this entry

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Wed, 18 Feb 2009