Fail to start VM from ISO

##### ISSUE TYPE

* Bug Report

##### COMPONENT NAME

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Secondary Storage
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##### CLOUDSTACK VERSION

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CloudStack 4.18.1.0
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##### CONFIGURATION

XCP-NG is used as hypervisor
Secondary storage connected via NFS
##### OS / ENVIRONMENT

##### SUMMARY

Hi!
I faced issue with ISO images.
Whe I mount ISO to multiple VMs, they stop starting in Cloudstack. And from the backend, I can see multiplying ISO SRs on every try to start VM. Some of them has ISO file inside, but most of them hasn't. Please look at screenshots attached.

My general question is can I safely remove (detach/foget/destroy) this empty SRs?
Even if I delete VM, ISO SRs still in the place.
Is there any way to fix issue with VM start?

Thank you in advance!

##### STEPS TO REPRODUCE

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##### EXPECTED RESULTS

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##### ACTUAL RESULTS

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未提供源文件、测试、命令或可复现的步骤。首先使用 CloudStack 4.18.1.0、XCP-NG 和基于 NFS 的辅助存储复现 VM 启动失败；当挂载 ISO 映像时 VMs 能够启动，且不会创建持久的空 ISO SRs，即视为完成。

由索引模型根据 Issue 内容生成。