Amazon EC2 Instance Storage

Instances that use Amazon EBS for the root device do not, by default, have instance store available at boot time. If you want to use the instance stores with your EBS-backed instance, you have to explicitly map the instance stores with the devices while launching the instance. Examples of mapping the instance stores with the devices are, dev/sdb=ephemeral0, dev/sdc=ephemeral1, and so on. You need to use command line tools for mapping the instance stores with the devices. For more information on device mapping, see Block Device Mapping

The following task list describes what you need to do to launch an EBS-backed m1.large Windows instance by mapping the instance stores with the devices.

The following task list describes what you need to do to launch an Amazon EBS-backed m1.large Linux instance by mapping the instance stores with the devices.

Instance stores can also be mapped to the devices while the AMI image is being created. When you map instance stores to the devices (while creating the AMI image), subsequent instances launched from that AMI will all have instance stores by default. These instance stores are available only for that instance. You will have to use command line tools for mapping the instance stores with the devices. For information on adding instance stores while creating an AMI image, see the section called “Creating Your Own AMIs”.

	Note
	You cannot map the instance stores with the devices after you've launched the instance.

No matter how you get your instance storage device on your instance, any data on those stores is deleted if the instance stops, fails, or terminates (except for data on the Amazon EBS volume being used as a root device).

	Tip
	Do not rely on your instance's instance storage for valuable, long-term data. Use a replication strategy across multiple instances to keep your data safe, or store your persistent data in Amazon S3, or use an Amazon EBS volume.

Instances that use Amazon S3 for the root device automatically have instance store available on them (for the root partition and other data you want to add). Instance stores on Amazon EC2 instance store-backed instances are visible and available from within a running instance.

The following task list describes what you need to do to access the instance stores from within an Amazon EC2 instance store-backed m1.large Windows instance.

Depending on the instance type, some instance stores on Amazon EC2 instance store-backed Linux and UNIX instances are not mounted. For example, on an m1.large Linux and UNIX instance, the device /dev/sdc, although formatted and available, has to be mounted before it can be used.

The following task list describes what you need to do to access the instance stores from within Amazon EC2 instance store-backed m1.large Linux instance.

You can use command line tools to prevent a particular instance storage device from attaching to the instance. You can do this for both Amazon EC2 instance store-backed and Amazon EBS-backed AMIs and instances. For example, mapping /dev/sdc=none when launching an instance will cause the device /dev/sdc to not attach to the instance. For more information on device mapping, see see Block Device Mapping and AMI Mapping Override.

Because Amazon EBS-backed AMIs include a root device volume, they don't include any default instance store (i.e., ephemeral storage) the way Amazon EC2 instance store-backed AMIs do. However, you might want instances launched from your Amazon EBS-backed AMIs to include instance storage by default. This section describes how to create an AMI that includes the instance storage of your choice by default. You must do this with the command line tools or API; there's currently no way to do it through the AWS Management Console.

API

You can use RegisterImage and specify a block device mapping that includes the instance storage that you want for the image.

To add instance storage by default

• Issue the following Query request to register the image. The example registers an AMI with an 80 GiB root device volume at /dev/sda1 created from the snap-12345678 snapshot. The root volume's deleteOnTermination flag is set to false. The second block device mapping in the request maps /dev/sdc to the ephemeral0 instance store.

  	Note
  	You can omit the size in the block device mapping if you want to create a volume the size of the snapshot. If you do specify a size, it must be equal to or larger than the snapshot.

  https://ec2.amazonaws.com/
  ?Action=RegisterImage
  &Name=MyImage
  &KernelId=aki-f70657b2
  &RamdiskId=ari-ff0d5cba
  &RootDeviceName=/dev/sda1
  &BlockDeviceMapping.1.DeviceName=/dev/sda1
  &BlockDeviceMapping.1.Ebs.SnapshotId=snap-12345678
  &BlockDeviceMapping.1.Ebs.VolumeSize=80
  &BlockDeviceMapping.1.Ebs.DeleteOnTermination=false
  &BlockDeviceMapping.2.DeviceName=/dev/sdc
  &BlockDeviceMapping.2.VirtualName=ephemeral0
  &...auth parameters...

  For information about the auth parameters, go to Common Query Parameters in the Amazon Elastic Compute Cloud API Reference.

  Following is an example response.

  <RegisterImageResponse xmlns="http://ec2.amazonaws.com/doc/2011-12-15/">
     <imageId>ami-61a54008</imageId>
  </RegisterImageResponse>

Any instance you then launch of the AMI includes the instance storage you specified. You can view the block device mappings for the instance. Unfortunately, the information that's available doesn't include the instance storage mappings. You can confirm the local storage devices are available from within the instance itself.For more information, see Viewing Block Device Mappings).

Disk Performance Optimization

Because of the way that Amazon EC2 virtualizes disks, the first write to any location on an instance's drives performs more slowly than subsequent writes. For most applications, amortizing this cost over the lifetime of the instance is acceptable. However, if you require high disk performance, we recommend that you initialize your drives by writing once to every drive location before production use. If you require further improvements in latency or throughput, we recommend using Amazon EBS.

To initialize the stores, use the following Linux/UNIX dd commands, depending on which store you want to initialize (/dev/sdb, etc.).

	Note
	Make sure to unmount the drive before performing this command. Initialization can take a long time (about 8 hours for an extra large instance).

To initialize the stores, use the following commands on the m1.large, m1.xlarge, c1.xlarge, m2.xlarge, m2.2xlarge, and m2.4xlarge instance types:

dd if=/dev/zero of=/dev/sdb bs=1M          
               dd if=/dev/zero of=/dev/sdc bs=1M          
               dd if=/dev/zero of=/dev/sdd bs=1M          
               dd if=/dev/zero of=/dev/sde bs=1M 

For information about the stores that are available for each instance type, see Instance Stores Available On Instance Types.

To perform initialization on all drives at the same time, use the following command:

dd if=/dev/zero bs=1M|tee /dev/sdb|tee /dev/sdc|tee /dev/sde > /dev/sdd

RAID Configuration

Configuring drives for RAID initializes them by writing to every drive location. When configuring software-based RAID, make sure to change the minimum reconstruction speed:

echo $((30*1024)) > /proc/sys/dev/raid/speed_limit_min