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# Storage Backends

S3QL supports different backends to store data at different service providers and using different protocols. A storage url specifies a backend together with some backend-specific information and uniquely identifies an S3QL file system. The form of the storage url depends on the backend and is described for every backend below.

All storage backends respect the `http_proxy` and `https_proxy` environment variables.

## Google Storage

Google Storage is an online storage service offered by Google. To use the Google Storage backend, you need to have (or sign up for) a Google account, and then activate Google Storage for your account. The account is free, you will pay only for the amount of storage and traffic that you actually use. Once you have created the account, make sure to activate legacy access.

To create a Google Storage bucket, you can use e.g. the Google Storage Manager. The storage URL for accessing the bucket in S3QL is then

    gs://<bucketname>/<prefix>

Here bucketname is the name of the bucket, and prefix can be an arbitrary prefix that will be prepended to all object names used by S3QL. This allows you to store several S3QL file systems in the same Google Storage bucket.

Note that the backend login and password for accessing your Google Storage bucket are not your Google account name and password, but the Google Storage developer access key and Google Storage developer secret that you can manage with the Google Storage key management tool.

## Amazon S3

Amazon S3 is the online storage service offered by Amazon Web Services (AWS). To use the S3 backend, you first need to sign up for an AWS account. The account is free, you will pay only for the amount of storage and traffic that you actually use. After that, you need to create a bucket that will hold the S3QL file system, e.g. using the AWS Management Console. For best performance, it is recommend to create the bucket in the geographically closest storage region, but not the US Standard region (see below).

The storage URL for accessing S3 buckets in S3QL has the form

    s3://<bucketname>/<prefix>

Here bucketname is the name of the bucket, and prefix can be an arbitrary prefix that will be prepended to all object names used by S3QL. This allows you to store several S3QL file systems in the same S3 bucket.

Note that the backend login and password for accessing S3 are not the user id and password that you use to log into the Amazon Webpage, but the AWS access key id and AWS secret access key shown under My Account/Access Identifiers.

### Reduced Redundancy Storage (RRS)

S3QL does not allow the use of reduced redundancy storage. The reason for that is a combination of three factors:

- RRS has a relatively low reliability, on average you lose one out of every ten-thousand objects a year. So you can expect to occasionally lose some data.
- When `fsck.s3ql` asks S3 for a list of the stored objects, this list includes even those objects that have been lost. Therefore `fsck.s3ql` can not detect lost objects and lost data will only become apparent when you try to actually read from a file whose data has been lost. This is a (very unfortunate) peculiarity of Amazon S3.
- Due to the data de-duplication feature of S3QL, unnoticed lost objects may cause subsequent data loss later in time (see Data Durability for details).

## OpenStack/Swift

OpenStack is an open-source cloud server application suite. Swift is the cloud storage module of OpenStack. Swift/OpenStack storage is offered by many different companies.

The storage URL for the OpenStack backend has the form

    swift://<hostname>[:<port>]/<container>[/<prefix>]

Note that the storage container must already exist. Most OpenStack providers offer a web frontend that you can use to create storage containers. prefix can be an arbitrary prefix that will be prepended to all object names used by S3QL. This allows you to store several S3QL file systems in the same container.

The OpenStack backend always uses HTTPS connections. Note, however, that at this point S3QL does not verify the server certificate (cf. issue 267).

## RackSpace CloudFiles

RackSpace CloudFiles uses OpenStack internally, so you can use the OpenStack/Swift backend (see above). The hostname for CloudFiles containers is `auth.api.rackspacecloud.com`. Use your normal RackSpace user name for the backend login, and your RackSpace API key as the backend passphrase. You can create a storage container for S3QL using the Control Panel (go to Cloud Files under Hosting).

Warning

As of January 2012, RackSpace does not give any information about data consistency or data durability on their web page. However, RackSpace support agents (especially in the live chat) often claim very high guarantees. Any such statement is wrong. As of 01/2012, RackSpace CloudFiles does not give any durability or consistency guarantees (see Important Rules to Avoid Losing Data for why this is important). Why this fact is only acknowledged RackSpace’s technical engineers, and/or not communicated to their sales agents is not known.

You should note that opinions about RackSpace differ widely among S3QL users and developers. On one hand, people praise RackSpace for their backing of the (open source) OpenStack project. On the other hand, their heavily advertised “fanatical support” is in practice often not only less than helpful, but their support agents also seem to be downright incompetent. However, there are reports that the support quality increases dramatically once you are a customer and use the “Live Chat” link when you are logged into the control panel.

## S3 compatible

The S3 compatible backend allows S3QL to access any storage service that uses the same protocol as Amazon S3. The storage URL has the form

    s3c://<hostname>:<port>/<bucketname>/<prefix>

Here bucketname is the name of an (existing) bucket, and prefix can be an arbitrary prefix that will be prepended to all object names used by S3QL. This allows you to store several S3QL file systems in the same bucket.

## Local

S3QL is also able to store its data on the local file system. This can be used to backup data on external media, or to access external services that S3QL can not talk to directly (e.g., it is possible to store data over SSH by first mounting the remote system using `sshfs`_ and then using the local backend to store the data in the sshfs mountpoint).

The storage URL for local storage is

    local://<path>

Note that you have to write three consecutive slashes to specify an absolute path, e.g. `local:///var/archive`. Also, relative paths will automatically be converted to absolute paths before the authentication file (see Storing Authentication Information) is read, i.e. if you are in the `/home/john` directory and try to mount `local://s3ql`, the corresponding section in the authentication file must match the storage url `local:///home/john/s3ql`.

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