GCP ACE Prep

The Two Main Storage Paradigms

The first step in choosing storage is to identify the type of data and access pattern. GCP storage options fall into two main categories.

• Block Storage (Persistent Disk): Think of this as a virtual hard drive (like a USB drive or an internal SSD) that you attach to a single Compute Engine VM. It's used for the operating system, databases, or any application running on a VM that needs a filesystem.
• Object Storage (Cloud Storage): Think of this as a massively scalable "file cabinet" in the cloud. You store individual files (objects) like images, videos, backups, and documents. It's accessed via an API, not mounted as a drive.

Block Storage: Persistent Disk (PD)

Persistent Disk provides reliable, high-performance block storage for your Compute Engine instances. The key decision for the ACE exam is choosing between Zonal and Regional availability.

            graph TD
                subgraph "Region: us-central1"
                    subgraph "Zone: us-central1-a"
                        VM_A(VM in Zone A)
                        ZonalPD(Zonal PD)
                        VM_A -- Attaches to --> ZonalPD
                    end
                    subgraph "Zone: us-central1-b"
                        Replica(Regional PD Replica)
                    end
                    RegionalPD(Regional PD
in Zone A)
                    VM_A -- Attaches to --> RegionalPD
                    RegionalPD -- Synchronously Replicates --> Replica
                end
            

1. Zonal Persistent Disk

• What it is: A standard PD that lives in a single zone.
• Performance: Higher performance and lower latency than regional PD.
• Cost: Less expensive.
• The Catch: If its zone becomes unavailable, the disk is also unavailable until the zone recovers.
• When to use it: The default choice for most workloads. Use it for standard VMs, databases where you handle replication at the application level, or in Managed Instance Groups where the loss of a single VM/zone is acceptable.

2. Regional Persistent Disk

• What it is: A highly available PD that is synchronously replicated between two zones in the same region.
• Performance: Slightly lower performance due to the overhead of cross-zone replication.
• Cost: More expensive than zonal PD.
• The Benefit: If the primary zone fails, you can force-attach the disk to a VM in the secondary zone, allowing your service to recover quickly.
• When to use it: For critical, stateful, single-instance workloads where you cannot afford downtime during a zonal failure (e.g., a critical SQL database that is not set up in a high-availability cluster).

Object Storage: Cloud Storage Classes

Cloud Storage offers different "storage classes" for your data. The choice depends entirely on how frequently you plan to access the data.

Decision Flowchart for Storage Selection

graph TD
    A{Start: What kind of data?} --> B{Is it for a VM filesystem - Block Storage?};
    B -- Yes --> C{Does the disk itself need to survive a zonal failure?};
    C -- Yes --> D[Regional Persistent Disk];
    C -- No --> E[Zonal Persistent Disk];

    B -- No, it's files/objects --> F{How often will you access the data?};
    F -- Frequently --> G[Standard Storage];
    F -- About once a month --> H[Nearline Storage];
    F -- About once a quarter --> I[Coldline Storage];
    F -- About once a year or less --> J[Archive Storage];

    style D fill:#2E7D32, color:white
    style E fill:#2E7D32, color:white
    style G fill:#2E7D32, color:white
    style H fill:#2E7D32, color:white
    style I fill:#2E7D32, color:white
    style J fill:#2E7D32, color:white

            

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