Dell EMC Unity: Small files affect NDMP restore speeds (User Correctable)

Summary: This article covers the expectations of NDMP restores and which considerations to have towards it's Theory of Operation alongside Unity NAS Servers, having particular attention to its behavior when restoring a very large amount of small files. ...

This article applies to This article does not apply to This article is not tied to any specific product. Not all product versions are identified in this article.
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Symptoms

NDMP Restore from a File System to another, on the same NAS Server, is not as per expectations:
  • Unity Administrator's expectations were the maximum allowed of the tape drive, which was around 350MB/s,
  • Unity Administrator's expectations are that 200MB/s in average should be at least possible,
  • Current obtained speeds are:   ~650GB in ~4.5h at ~40MB/s,
  • Performance is not affecting actual File Sharing, there's no Data Unavailability.
  • Can be mistaken as a connectivity bottleneck by third party technical groups (Host/Client Providers).

Cause

Known causes for slow speeds in NDMP Restores:
  1. The amount and size of the data backed.
  2. Large amount of small sized files. 
  3. The NDMP restore is triggered from Data Migration Assistant (DMA) Graphical User Interface (GUI) rather than the DMA  Command Line Interface (CLI).
  4. Limitations within the third party Tool/Host being used.

Resolution

Restore will be slow when there are large amounts of small size files, because each file would have some additional time effort due to file creation.
Please know this is Function As Design (FAD).

For a detailed analysis on your particular issue, please contact Technical Support and reference Article Number 000185519.

Additional Information

To confirm you are experiencing the same scenario, please verify and run this command:
  1. Immediately after your Restore has been triggered,
  2. And then 3 times following that, 10 minutes apart:
Command: svc_pax ALL -stats -verbose 

Here's an example of an output which shows a very large amount of tiny files: 
service@spa:~/user# svc_pax ALL -stats -verbose 
dir or 0 size file processed: 30647   
1 – 8KB size file processed: 302378 ----------------> Millions of tiny files
8KB+1 – 16KB size file processed: 50567
16KB+1 – 32KB size file processed: 36579
32KB+1 – 64KB size file processed: 27080
64KB+1 – 1MB size file processed: 53438
1MB+1 – 32MB size file processed: 7630
32MB+1 – 1GB size file processed: 218
1G more size file processed: 3

Affected Products

Dell Unity 300, Dell EMC Unity 300F, Dell EMC Unity 350F, Dell EMC Unity 400, Dell EMC Unity 400F, Dell EMC Unity 450F, Dell EMC Unity 500, Dell EMC Unity 500F, Dell EMC Unity 550F, Dell EMC Unity 600

Products

Dell EMC Unity XT 380, Dell EMC Unity XT 380F, Dell EMC Unity XT 480, Dell EMC Unity XT 480F, Dell EMC Unity 600F, Dell EMC Unity 650F, Dell EMC Unity XT 680, Dell EMC Unity XT 680F, Dell EMC Unity XT 880, Dell EMC Unity XT 880F , Dell EMC Unity Family |Dell EMC Unity All Flash, Dell EMC Unity Family, Dell EMC Unity Hybrid ...
Article Properties
Article Number: 000185519
Article Type: Solution
Last Modified: 11 ديسمبر 2025
Version:  5
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