Amazon Elastic Block Store (EBS)Amazon Elastic Block Store (EBS) provides block level storage volumes for use with Amazon EC2 instances. Amazon EBS volumes are off-instance storage that persists independently from the life of an instance. Amazon Elastic Block Store provides highly available, highly reliable storage volumes that can be attached to a running Amazon EC2 instance and exposed as a device within the instance. Amazon EBS is particularly suited for applications that require a database, file system, or access to raw block level storage. Easy to sign up,
pay only for what you use 
Features of Amazon EBS volumes
Using Amazon EBS VolumesAmazon EBS volumes are created in a particular Availability Zone and can be from 1 GB to 1 TB in size. Once a volume is created, it can be attached to any Amazon EC2 instance in the same Availability Zone. Once attached, it will appear as a mounted device similar to any hard drive or other block device. At that point, the instance can interact with the volume just as it would with a local drive, formatting it with a file system or installing applications on it directly. A volume can only be attached to one instance at a time, but many volumes can be attached to a single instance. This means that you can attach multiple volumes and stripe your data across them for increased I/O and throughput performance. This is particularly helpful for database style applications that frequently encounter many random reads and writes across the dataset. If an instance fails or is detached from an Amazon EBS volume, the volume can be attached to any other instance in that Availability Zone. Amazon EBS volumes can also be used as boot partitions for Amazon EC2 instances, which allows you to increase the size of your boot partition up to 1 TB, preserve your boot partition data beyond the life of your instance, and bundle your AMI in one-click. You can also stop and restart instances that boot from Amazon EBS volumes while preserving state, with very fast start-up times. As with any use of Amazon EBS, you only pay for the amount of resources you consume. Amazon EBS SnapshotsAmazon EBS provides the ability to back up point-in-time snapshots of your data to Amazon S3 for durable recovery. Amazon EBS snapshots are incremental backups, meaning that only the blocks on the device that have changed since your last snapshot will be saved. If you have a device with 100 GBs of data, but only 5 GBs of data has changed since your last snapshot, only the 5 additional GBs of snapshot data will be stored back to Amazon S3. Even though the snapshots are saved incrementally, when you delete a snapshot, only the data not needed for any other snapshot is removed. So regardless of which prior snapshots have been deleted, all active snapshots will contain all the information needed to restore the volume. In addition, the time to restore the volume is the same for all snapshots, offering the restore time of full backups with the space savings of incremental. Snapshots can also be used to instantiate multiple new volumes, expand the size of a volume or move volumes across Availability Zones. When a new volume is created, there is the option to create it based on an existing Amazon S3 snapshot. In that scenario, the new volume begins as an exact replica of the original volume. By optionally specifying a different volume size or a different Availability Zone, this functionality can be used as a way to increase the size of an existing volume or to create duplicate volumes in new Availability Zones. If you choose to use snapshots to resize your volume, you need to be sure your file system or application supports resizing a device. New volumes created from existing Amazon S3 snapshots load lazily in the background. This means that once a volume is created from a snapshot, there is no need to wait for all of the data to transfer from Amazon S3 to your Amazon EBS volume before your attached instance can start accessing the volume and all of its data. If your instance accesses a piece of data which hasn’t yet been loaded, the volume will immediately download the requested data from Amazon S3, and then will continue loading the rest of the volume’s data in the background. Amazon EBS shared snapshots allows you to share these snapshots, making it easy for you to share this data with your co-workers or others in the AWS community. With this feature, users that you have authorized can quickly use your Amazon EBS shared snapshots as the basis for creating their own Amazon EBS volumes. If you choose, you can also make your data available publicly to all AWS users. Users to whom you have granted access can create their own EBS volumes based on your snapshot; your original snapshot will remain intact. This is a great way for developers to easily share data with the rest of the Amazon EC2 community, and makes it easy for new customers to create Amazon EBS volumes from an existing snapshot. Because all the data is stored in the Amazon cloud, users don’t have to wait for time consuming downloads, and can access it within minutes. How to share snapshotsSnapshots can be shared using AWS Management Console or using API calls. You have full control over what accounts you share each snapshot with, including the option to share it with the entire AWS community. AWS Management Console:
Amazon EBS Volume PerformanceThe latency and throughput of Amazon EBS volumes is designed to be significantly better than the Amazon EC2 instance stores in nearly all cases. You can also attach multiple volumes to an instance and stripe across the volumes. This is one way to improve I/O rates, especially if your application performs a lot of random access across your data set. The exact performance will depend on the application (e.g. random vs. sequential I/O or large vs. small request sizes), so the best measure is to benchmark your real applications against the volume. Because Amazon EBS volumes require network access, you will see faster and more consistent throughput performance with larger instances. Amazon EBS Volume DurabilityAmazon EBS volumes are designed to be highly available and reliable. Amazon EBS volume data is replicated across multiple servers in an Availability Zone to prevent the loss of data from the failure of any single component. The durability of your volume depends both on the size of your volume and the percentage of the data that has changed since your last snapshot. As an example, volumes that operate with 20 GB or less of modified data since their most recent Amazon EBS snapshot can expect an annual failure rate (AFR) of between 0.1% – 0.5%, where failure refers to a complete loss of the volume. This compares with commodity hard disks that will typically fail with an AFR of around 4%, making EBS volumes 10 times more reliable than typical commodity disk drives. Because Amazon EBS servers are replicated within a single Availability Zone, mirroring data across multiple Amazon EBS volumes in the same Availability Zone will not significantly improve volume durability. However, for those interested in even more durability, Amazon EBS provides the ability to create point-in-time consistent snapshots of your volumes that are then stored in Amazon S3, and automatically replicated across multiple Availability Zones. So, taking frequent snapshots of your volume is a convenient and cost effective way to increase the long term durability of your data. In the unlikely event that your Amazon EBS volume does fail, all snapshots of that volume will remain intact, and will allow you to recreate your volume from the last snapshot point. Projecting CostsWith Amazon Elastic Block Store, you only pay for what you use. Volume storage is charged by the amount you allocate until you release it, and is priced at a rate of $0.10 per allocated GB per month Amazon EBS also charges $0.10 per 1 million I/O requests you make to your volume. Programs like IOSTAT can be used to measure the exact I/O usage of your system at any time. However, applications and operating systems often do different levels of caching, so you will likely see a lower number of I/O requests on your bill than is seen by your application unless you sync all of your I/Os to disk. As an example, a medium sized website database might be 100 GB in size and expect to average 100 I/Os per second over the course of a month. This would translate to $10 per month in storage costs (100 GB x $0.10/month), and approximately $26 per month in request costs (~2.6 million seconds/month x 100 I/O per second * $0.10 per million I/O). Snapshot storage is based on the amount of space your data consumes in Amazon S3. Because data is compressed before being saved to Amazon S3, and Amazon EBS does not save empty blocks, it is likely that the size of a snapshot will be considerably less than the size of your volume. For the first snapshot of a volume, Amazon EBS will save a full copy of your data to Amazon S3. However for each incremental snapshot, only the part of your Amazon EBS volume that has been changed will be saved to Amazon S3. Volume data is broken up into chunks before being transferred to Amazon S3. While the size of the chunks could change through future optimizations, the number of PUTs required to save a particular snapshot to Amazon S3 can be estimated by dividing the size of the data that has changed since the last snapshot by 4MB. Conversely, when loading a snapshot from Amazon S3 into and Amazon EBS volume, the number of GET requests needed to fully load the volume can be estimated by dividing the full size of the snapshot by 4MB. You will also be charged for GETs and PUTs at normal Amazon S3 rates. |
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