Skip to main content
NetApp Response to Russia-Ukraine Cyber Threat
In response to the recent rise in cyber threat due to the Russian-Ukraine crisis, NetApp is actively monitoring the global security intelligence and updating our cybersecurity measures. We follow U.S. Federal Government guidance and remain on high alert. Customers are encouraged to monitor the Cybersecurity and Infrastructure Security (CISA) website for new information as it develops and remain on high alert.
NetApp Knowledge Base

E-Series: How does the Thin Volume feature works?

Views:
877
Visibility:
Public
Votes:
0
Category:
e-series-systems
Specialty:
esg
Last Updated:

 

Applies to

  • E-Series with TPV (Thin Provisioned Volumes) enabled
  • DDP
  • Hosts having the UNMAP feature enabled
  • TRIM

Answer

  1. Host sends an UNMAP command to reclaim unused storage blocks on the E-series TPV enabled volume
  2. The 64KB clusters in the TPV are immediately marked as “free”. These free clusters in the index will be used first to prevent further repository growth on host writes.
  3. When there are “enough” free clusters -which is dependent on the repository size- periodic defrag scans will shift the free clusters together into contiguous 4GB C-stripes that can be freed and returned to the pool (min of 4GB at a time, but this varies depending on the size of repository and UNMAP operation).
  4. Depending on the number of unused storage blocks to be reclaimed and the size of repository,  different goals and thresholds for the defrag scans will be set.
  5. Data may not go back to the DDP for a while since these scans are specifically throttled to maintain an acceptable performance penalty. When the scans reach their target based of the repository size, the number of blocks to be reclaimed, it will give the freed C-stripes back to the DDP. It’s also worth noting that the freed clusters can still be reused by the  TPV even though they haven’t been given back to the DDP via repository TRIM.

Additional Information

The way TPVs work internally is often a cause for confusion for customers as UNMAP operations issued on the host will not always result in space being returned to the DDP.

 

Scan to view the article on your device