Hello I have an sc2020 and right now I have the error message Message 1 of 2 - One of the storage types is in emergency mode (out of disk space)
I don't any other disks. I have a snapshot overhead about 5T.
So I was searching how I can release snapshots. I couldn't find anything in Dell Storage Manager.
I have Dell Storage Manager 2016 R3.11 Build 18.104.22.168
Can you help me please.
The snapshot overhead is the amount of space used to store frozen data where changes have occurred.
Lets say you have an empty volume.
You write 1GB of data to it. This goes in to the Volume and is stored in the first tier or RAID-10.
A snapshot is taken all 1GB is progressed to the next tier or RAID-6.
The system is still running and changes 200MB of the 1GB of data.
These changes go into RAID-10 as before, but the old copy of the data is still in the snapshot at RAID-6. SO you now have a 200MB snapshot overhead, because it is holding 200MB of stale data, i.e. its been changed since the snapshot was taken.
I think that is a very simplified description. The situation gets quite a bit more complicated when you have multiple snapshots of a Volume.
Minimising the snapshot overhead can be achieved by increasing the snapshot frequency and reducing the expiry time. On our systems we snapshot every two hours and expire them in two hours, so we don't have any more than one snapshot in the system at a time, and the amount of change possible in two hours means the RAID-10 occupancy is minimised.