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According to AWS I got 850 GB storage with the Medium EC2 server. But when i create an Amazon Linux AMI, I am unable to use the 850 GB provided.

While creating it does show in Storage Device Configuration in Instance Store Volumes that its device will be located at /dev/sdb , but when I start the VM , I just find /dev/sda1.

Can you please help me in mounting this storage? Thank You

Also, when Amazon claims that instance storage is not safe for long term use and should prefer using EBS, then what is the point of those 850 GB?

Thanks

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What specific instance type are you trying to run? c1.medium? m1.medium? something else? –  Eric Hammond Oct 1 '12 at 23:34
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Here are two great resources for learning about instance storage on EC2: docs.amazonwebservices.com/AWSEC2/latest/UserGuide/… and docs.amazonwebservices.com/AWSEC2/latest/UserGuide/… –  Eric Hammond Oct 1 '12 at 23:56

2 Answers 2

up vote 4 down vote accepted

The use of instance-local storage that is not persistent when an instance is stopped is pretty simple: It's a very large chunk of space useful for transient things. They're the perfect target for mounting to /tmp, and is extremely useful if your server handles very large files transiently.

For example, if you were building a group of instances to do voice-to-text translation of uploaded video-files, instance-local storage would be just the thing you want to put the in-process files on. It may be there for a few hours while the file is processed, but once it's done it can be deleted and another one taken up. You don't need EBS for that, and it's a lot cheaper to run that kind of storage out of instance-local rather than EBS.

Instance-local storage is meant to be used as scratch-space for running processing, not long-term storage. If your workload doesn't use scratch-space for anything, or what it needs is so small as to not be significant, then it isn't a good fit for you.

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Ephemeral storage or instance-store DOES persist across reboots of an instance! It does not persist across a stop/start, nor a termination, nor some instance hardware failures. Here's an article I wrote on the difference between reboot and stop/start: alestic.com/2011/09/ec2-reboot-stop-start –  Eric Hammond Oct 1 '12 at 23:29

If it's not already mounted under e.g. /mnt and if it doesn't have a filesystem created already then do:

  1. Check the device name

    sudo fdisk -l

  2. Make directory to where you want to mount the volume

    sudo mkdir /mnt

  3. Create filesystem on your volume (make sure you choose the correct volume because this creates a new file system on the volume)

    sudo mkfs.ext4 /dev/xvdj

  4. Mount volume

    sudo mount -t ext4 /dev/xvdj /mnt

  5. If you want to preserve the mount after e.g. a restart, open /etc/fstab and add the mount to it

    echo "/dev/xvdj /mnt auto noatime 0 0" | sudo tee -a /etc/fstab

  6. Make sure nothing is wrong with fstab by mounting all

    mount -a

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Depending on the instance type, you first need to attach the instance store volumes to the instance by using the block-device-mapping options. If you don't do this, you may not even see the devices under /dev –  Eric Hammond Oct 1 '12 at 23:32
    
@EricHammond's comment was really the answer to my quest - I didn't see them anywhere - even in fdisk -l –  Peter V. Mørch Nov 24 at 23:45

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