SC Storage Customer Notification: 7.3 Conservation / Emergency Mode Changes

Summary: The purpose of this document is to assist customers in understanding the changes to Storage Center OS (SCOS) 7.3 pertaining to Conservation / Emergency Mode.

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Instructions

The purpose of this document is to assist customers in understanding the changes to Storage Center OS (SCOS) 7.3 pertaining to Conservation / Emergency Mode.What goals are the Improvements attempting to accomplish?
  1. Extend the time between Conservation Mode and Emergency Mode to allow for greater ability to take action before Emergency Mode occurs.
  2. Make system low space conditions more visible via alerts / notifications.
  3. Provide a better balance of RAID 10 Vs. Parity space on the system to prevent too much unused RAID 10 space.
 
Details behind each improvement goal
  1. Extending the time between Conservation Mode and Emergency Mode
    1. Change the Conservation Mode threshold limit
    • Pre SCOS 7.3 Conservation Mode threshold limit - allocated pool free space falls below 16GB
    • Post SCOS 7.3 Conservation Mode threshold limit - allocated pool free space falls below 0.5% with a floor of 100 GB and a ceiling of 2 TB
    • Most Storage Center systems will effectively have a Conservation Mode threshold of around 100 GB 
    1. When entering Conservation Mode, Storage Center enables a volume QOS slowing page consumption
    2. Change how snapshots are handled while in Conservation Mode
      • Pre SCOS 7.3 - snapshots were automatically expired
      • Post SCOS 7.3 - automatic snapshot expiration no longer occurs as this will provide a recovery buffer in case the system does enter Emergency Mode
  2. Improved messaging for low space conditions
    1. Conservation Mode alerts will now occur daily while the system is in Conservation Mode
    2. When the Disk Folder runs low on free space, an alert will generate at each % change: 10%, 9%, 8%, 7%, etc as the free space decreases. 
    3. New banner in DSM and Unisphere that asks the user to acknowledge the message that they are low on free space.
  3. Automatically balance the pool space usage between RAID 10 and Parity space 
    1. System will routinely examine the space usage by volumes and the space allocation of the pool to determine if there is more RAID 10 space allocated than needed and if so, take corrective action.
    • Take Space Management Snapshots on volumes that have a large amount of RAID 10 data.  This will invoke On Demand Data Progression to coerce RAID 10 data to move to parity
    • Then remove freed up RAID 10 allocations to return as unallocated space in the pool.  This can later be used as Parity space allocations.
    • RAID 10 space will continue to be transitioned to parity until a clear threshold is met and then stop the corrective action.
    1. This addresses issues where the importing of volumes or performing some other operation that caused the storage pool to be filled up with RAID 10 space and therefore unable to replace RAID 10 allocations with Parity allocations​​​​​​​.  

 

Affected Products

Entry Level & Midrange, Compellent (SC, SCv & FS Series), Dell Compellent SC4020, Dell Storage SC8000, Dell Storage SCv2000, Dell Storage SCv2020, Dell Storage SCv2080, Dell Storage SC5020, Dell Storage SC5020F, Dell Storage SC7020 , Dell Storage SC7020F, Dell Storage SC9000, Dell Storage SCv3000, Dell Storage SCv3020 ...
Article Properties
Article Number: 000114804
Article Type: How To
Last Modified: 21 Feb 2021
Version:  3
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