Applicable Products
- HDP for Business
- Proxmox VE
Symptom
You back up a Proxmox virtual machine with HDP for Business more than once. In Activities, the Backup Type column shows Full for every backup, including backups after the first one. Each backup takes about the same amount of time and consumes as much storage space as a full backup, even though you expect subsequent backups to be incremental.
Root Cause
Incremental backups of a Proxmox virtual machine rely on Changed Block Tracking (CBT). CBT records which disk blocks have changed since the previous backup, so that HDP for Business only needs to transfer those blocks.
Whether CBT data survives a shutdown of the virtual machine depends on the disk format:
| Disk format | CBT persistence | Backup behavior after the virtual machine is powered off |
|---|
| Native qcow2 | Persistent | CBT data is retained. The next backup is incremental. |
| raw | Not persistent | CBT data is lost. The next backup falls back to a full backup. |
| vmdk | Not persistent | CBT data is lost. The next backup falls back to a full backup. |
If a virtual machine that uses a raw or vmdk disk is powered off between two backups, HDP for Business cannot determine which blocks have changed and therefore performs a full backup instead. This is a limitation of the underlying CBT mechanism, not a defect of the backup feature.
Recommendation
- Use the native qcow2 disk format for virtual machines that you back up regularly. Only qcow2 supports persistent CBT and can therefore continue to run incremental backups after a power off.
- If a virtual machine must use a raw or vmdk disk, keep it powered on between backups so that its CBT data remains available.
- Expect the first backup after any power off of a raw or vmdk virtual machine to be a full backup. Plan the backup window and the storage capacity of the backup destination accordingly.
Further Reading
适用产品
- HDP for Business
- Proxmox VE
症状
您使用 HDP for Business 多次备份 Proxmox 虚拟机。在活动中，备份类型列显示每次备份都是完整，包括较高次备份后的备份。每次备份所需时间相同，并消耗与完整备份相同的存储空间，即使您期望后续备份为增量备份。
根本原因
Proxmox 虚拟机的增量备份依赖于更改块跟踪 (CBT)。CBT 记录自上次备份以来哪些磁盘块发生了变化，以便 HDP for Business 只需传输这些块。
CBT 数据在虚拟机关闭后是否保留取决于磁盘格式：
| 磁盘格式 | CBT 持久性 | 虚拟机关闭后的备份行为 |
|---|
| 原生 qcow2 | 持久性 | CBT 数据被保留。下次备份为增量备份。 |
| raw | 不持久 | CBT 数据丢失。下次备份回退为完整备份。 |
| vmdk | 不持久 | CBT 数据丢失。下次备份回退为完整备份。 |
如果使用 raw 或 vmdk 磁盘的虚拟机在两次备份之间关闭，HDP for Business 无法确定哪些块发生了变化，因此执行完整备份。这是底层 CBT 机制的限制，而不是备份功能的缺陷。
建议
- 对于定期备份的虚拟机，使用原生 qcow2 磁盘格式。只有 qcow2 支持持久性 CBT，因此在断电后可以继续进行增量备份。
- 如果虚拟机必须使用 raw 或 vmdk 磁盘，请在备份之间保持其开机，以便其 CBT 数据保持可用。
- 预计 raw 或 vmdk 虚拟机在任何断电后的较高次备份为完整备份。请相应地规划备份窗口和备份目标的存储容量。
进一步阅读
