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SCv2020: Allocated Space - Configured Space = Mystery Space
We have 7 disks 279.4GB each giving 1.91TB Total Space. Total Space (1.91TB) - Spare Space (277.52GB) - Free Space (13.13GB) = 1.63TB (Allocated Space). For now it is clear. But from the allocated space a volume has been created by our vendor. Why its size is only 1TB (Configured Space)? What kind of data is located on the missing 0.63TB? This question bothers me for months and I can't figure it out. The vendor cannot explain that, but he assures the volume size is maximum we can get and it can be expanded only by Free Space (tiny 13.13GB). I asked a Dell Compellent specialist about that and he also is not able to explain that. It seems to be very strange being two specialists can't explain what is the purpose of the space, what kind of data is stored on the space if any. I attach a combined screenshot showing the situation. If there is someone able to explain it for me I would appreciate it.
Origin3k
4 Operator
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1.7K Posts
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March 15th, 2019 13:00
You have present 1TB to your Hosts which is the 1TB "configurated" value. As a high water mark the Hosts have written 688.65GB into that 1TB volume. Since the SC is thinprovisioning it doesnt use any space for the free 335GB.
You have 3 snapshots which adds 116GB (its a low change ratio) to the 688GB. You have RAID protection (Single or Dual Redundancy) and based on the assigned Storage Profile its a mix of RAID10 and RAID5 or RAID10DM and RAID6 or RAID5/6 for everything which adds another 201GB to the total consumtion is 1006.61GB right now.
The system expect that more Data is comming in because of the measurement from the past and your growing rate so it pre"allocate" some space to be prepared. The system will also move blocks between the RaidLevel.
With that dynamic RAID Level and the unknown changeratio the system can only predict what space is needed but canot give a precise answer.
Regards
Joerg
DELL-Bob Mi
230 Posts
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March 16th, 2019 09:00
In your first screen shot you are looking at the space usage from the 15K disk folder which can be misleading when trying to determine Volume space usage.
I would suggest to follow the steps on page 325 of the Dell Storage Manager Administrator’s Guide:
For each storage type, the data progression pressure report displays how space is allocated, consumed, and scheduled to move across different RAID types and storage tiers. Use the data progression pressure report to make decisions about the types of disks to add to a Storage Center.
1. Select a Storage Center from the Storage view. (Data Collector connected Storage Manager Client only)
2. Click the Storage tab.
3. In the Storage tab navigation pane, expand Storage Type, then select the individual storage type that you want to examine.
4. Click the Pressure Report subtab to view the data progression pressure report. By default, the most recent data gathered from the Storage Center is displayed.
5. (Optional) To view a previously generated data progression report, select a report from the drop-down menu. Reports are identified by the date and time at which they were generated.
Disk Space Available - Total amount of disk space available on the disks of a Storage Center
Disk Space Allocated - Total amount of disk space allocated on the disks
Disk Allocated - Space reserved for volumes.
Disk Used - From the amount of space allocated, the amount that is in use by volumes.
Volume Allocated - Amount of space reserved for use by volumes after RAID is applied.
Volume Used - Amount of space used by volumes after RAID is applied.
I feel this can give you a better view of what is allocated, used, and available.
Dell Storage Manager 2018 Administrators Guide page 325
https://topics-cdn.dell.com/pdf/dell-storage-manager_administrator-guide3_en-us.pdf
Undercover007
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March 18th, 2019 05:00
I think I got it. But if I do what about the the grey space in the bar titled "In the future (prediction, extrapolation)"? Will it become available at some point in the future when it becomes clear the data including snapshots and RAID won't use it?
DELL-Bob Mi: I saw your similar post in the forum and I saw the definitions in the official guide, but still it wasn't clear for me.
Thank you guys for your replies.