Why Does Drive Enumeration Change Between System Boots with Intel® Virtual RAID on CPU (Intel® VROC) RAID Volumes?
Content Type: Maintenance & Performance | Article ID: 000098840 | Last Reviewed: 09/20/2024
We noticed that drive enumeration in Intel VROC 7.8 and 8.0 changes every time the system boots. We need drives to be fixed for disaster recovery purposes. Can drive enumeration be fixed by Intel VROC?
Intel® VROC does not define how the drives and volumes are enumerated by the operating system during a system boot. The enumeration process really depends on how the hardware is organized, which varies from system to system.
It is all about timing. The devices that are initialized first get smaller numbers. In every system boot, there may be a race that does not always conclude the same way. That is why drive enumeration may be different between system boots.
There are multiple kernel drivers enumerating the drives, such as the inbox AHCI driver, the inbox NVMe driver, the Intel® VROC (SATA) driver, the Intel® VROC (VMD NVMe) driver, and so on. Those drivers can enumerate drives simultaneously, and depending on which driver reports first to the operating system, that order will be visible in the operating system.
Besides the drivers working simultaneously, the timing is also influenced by the complexity of the platform. Older systems are much simpler than new ones. In simpler systems, it is easier to have more consistent boot timing, which may translate into a consistent drive enumeration between system boots. This means that if a particular platform shows consistent drive enumeration between system boots, it does not necessarily mean a different platform will also show consistent drive enumeration.
Can the drive enumeration be fixed by the Intel® VROC driver? Not really. The Intel® VROC driver is only a small piece of this timing puzzle.
If you are developing your own monitoring tools, relying on fixed (hard coded) drive or volume index numbers is not recommended, as they may change between boots. Instead, the recommended approach is to query the drive/volume information to determine which disk number maps to which drive or volume.