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JimGandy avatar image
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JimGandy asked IanWatts-3532 answered

HCI/S2D Reserve capacity - Why is this not just automactic?

This is a problem for many of us. We run out of space in the Storage Pool and we do not know there is a problem until a disk fails or we see storage repair jobs failing. Is there a technical reason why Microsoft is not able to just reserve the equivalent of one capacity drive per server, up to 4 drives automictically at Storage Pool creation as described here
https://docs.microsoft.com/en-us/windows-server/storage/storage-spaces/plan-volumes#reserve-capacity?

azure-stack-hci
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ReevesLouis-9701 avatar image
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ReevesLouis-9701 answered

I also posted the similar question. I just noticed your post- so this is hopefully not going to become common- Hope MS will plan something for this-

https://answers.microsoft.com/en-us/insider/forum/insider_wintp-insider_repair/why-azure-stack-hci-s2d-hcios-reserve-capacity-is/e6be231b-60ac-4463-b171-76c24cf1f78a?tm=1619459006776

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CyrAz avatar image
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CyrAz answered

Because it's your absolute right to fill up all the space you have. But in that case you need to be able to quickly replace a failed drive...

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StevenEkren-7009 avatar image
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StevenEkren-7009 answered

https://docs.microsoft.com/en-us/windows-server/failover-clustering/health-service-faults

The following fault should be discoverable via Windows Admin Center, or by the PowerShell for getting faults described in that article. This is the description of the fault that shows:

Pool Capacity (1)
FaultType: Microsoft.Health.FaultType.StoragePool.InsufficientReserveCapacityFault

 Severity: Warning
 Reason: "The storage pool does not have the minimum recommended reserve capacity. This may limit your ability to restore data resiliency in the event of drive failure(s)."
 RecommendedAction: "Add additional capacity to the storage pool, or free up capacity. The minimum recommended reserve varies by deployment, but is approximately 2 drives' worth of capacity."
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JimGandy avatar image
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JimGandy answered

Is there an event in the event logs for this information?

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ReevesLouis-9701 avatar image
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ReevesLouis-9701 answered

It would be just common sense that a critical alert should be generated for the system event log. This is going to be a major problem for customers who don't realize the consequences of running out of space. You think this would be common sense, but in 2021 it is not. People think the pool will work fine, because there Virtual disk has free space. If the reserved capacity is gone or the pool has 1% free space, you should have gotten a a critical system event long ago, at say 10%. This 1% pool free space customer is about to crash!!!

Thank you,

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StevenEkren-7009 avatar image
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StevenEkren-7009 answered

@ReevesLouis-9701 There are 2 things you note. Pool reserve space and volume space. When you create a new volume with storage spaces it allocates a fixed amount of space from the storage pool. The reserve capacity of the storage pool is there to allow for a physical disk to fail and be able to start a rapair of the virtual disks (storage spaces/volumes) before the disk is replaced or brought back. You can allocate volumes and fill the stroage pool without a reserve and the only effect is repairs will only take place when the physical disks are all there.

What I believe you are referencing is running out of space on a volume. This is no different on storage spaces as any other disk exposed in Windows Server. The volume has a specific amount of space and if it gets filled up, it's filled until you can extend the volume or reduce the data in the volume. This is not storage spaces specific, any volume on any windows system is the same. There are tools out there that will monitor volume free space. Windows Admin Center in the cluster view, shows volumes and makes clear how much free space is there.

I hope this helps,
StevenEk@Microsoft.com

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IanWatts-3532 avatar image
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IanWatts-3532 answered

So I would love to adjust my reserve capacity to the MS-recommended specs. So.. where is this done? Not found in WAC. Set-StoragePool doesn't seem to have a param like that. If it can only be done when a pool is created, yet you can add storage to a pool later, that would affect recommended reserve capacity settings and would be rather shortsighted.

My own situation is I have plenty of free space, those before me may have expanded the pool with disks, but whatever the case is my reserve capacity is too low for recommended specs. It was noted on the Failover Cluster Validation Report, although was not a Warning or Error state and I would have missed seeing it if not for my cache disks also being too small and warning...

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