# Pouta ### Storage

# Storage in cPouta
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- Root disk and ephemeral storage
                        - Persistent volumes
                        - Object storage (Allas)
                        - Snapshots

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                        # Root disk and ephemeral storage
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- File storage, shown as volumes inside the VM
                        - Stored together with the VM
                        - Root contains the OS
                        - Ephemeral is for performance but should be considered unreliable
                        - Data is lost if the VM is deleted

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                            <img src="/img/sld-pouta-image47.png" alt="Root disk and ephemeral storage inside a VM.">
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                        # Persistent volumes
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- File storage, shown as a volume inside the VM
                        - Project-specific; can have multiple volumes
                        - Transferable to other projects
                        - Attachable to one VM at a time
                        - Fault-tolerant against disk/server failures and VM deletion or crashes
                        - But not against human error — no automatic backups

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                        # Object storage (Allas)
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- It is not a file storage ➡️ a different use case from the OS point of view
                          - Accessed through an API (a-commands)
                          - Access outside the VM at <https://allas.csc.fi>
                        - Default quota is 10 TiB
                        - Hard limits:
                          - 1 000 buckets / project
                          - 500 000 objects / bucket

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                        # File storage vs object storage
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**File storage**

- Hierarchical structure
                        - Flexible file access
                        - Integrates with the OS
                        - Limited scalability
                        - Manual management
                        - More expensive at large scale
                        - More restricted access over the network

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**Object storage**

- Highly scalable, massive amounts of unstructured data
                        - Flat namespace and object keys
                        - Easily accessible over the network
                        - No hierarchical structure / file semantics
                        - "download – modify – upload" model

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                        # Snapshots
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- Store the data of a VM or volume at a certain state
                        - A VM snapshot can be used to launch a new instance
                          - A VM snapshot does not contain ephemeral storage
                        - Take a snapshot of a VM that is in the powered-off state

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                            <img src="/img/sld-pouta-image50.png" alt="Taking a snapshot of a VM or volume.">
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Thank you

Joona Tolonen

servicedesk@csc.fi