Merge pull request d-run#441 from windsonsea/disks

[en] Add instance/diskstorage.md

Author: windsonsea

docs/zh/docs/en/zestu/images/diskstorage01.png

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+# Disk Storage
+
+Disk storage provides the foundational storage for container instances and is divided into **system disks** and **data disks**.
+
+## System Disk
+
+The system disk serves as the container's root filesystem (rootfs). d.run provides each container instance with **30 GB of free system disk space**. Key features include:
+
+- **Basic Functionality**: The system disk can be saved as an image. For details, see [Save Image](../myimages/image-save.md). After a restart, the container will use the saved image.
+- **Advanced Functionality**: Developer instance system disks offer persistent storage. Data and environment settings are preserved even after shutdown or reboot. Once a developer instance is deleted, the system disk storage will be cleared. (Contact your administrator if you wish to use this feature.)
+
+![System Disk View](../images/diskstorage01.png)
+
+## Data Disk
+
+The data disk is a persistent storage solution based on distributed block storage. Each instance receives **50 GB of free data disk space**. Upon creation, the data disk is automatically mounted at `/root/tmp` and is tightly coupled to the lifecycle of the instance—it is created and deleted along with the instance. Data disks can be expanded with paid plans but **cannot be shared between instances**.
+
+### Data Disk Expansion
+
+By default, the data disk can be expanded up to **200 GB**. For larger quotas, contact **400-002-6898**. Note that:
+
+- Disk expansion is **irreversible**; you cannot shrink the disk after increasing its size.  
+- Billing continues even if the instance is shut down.
+
+After a container instance is created, you can **upgrade the data disk multiple times** through the **Change Configuration** feature.